fix(i18n): every refusal the API answers is structured and said in the reader's language

~150 HTTPExceptions carried a hand-written English sentence as their detail,
shown verbatim under the Hungarian UI — in the blocking error dialog and on
every inline surface that printed HttpError.detail (sign-in, setup wizard,
change password, the passphrase gate, live search). Four also quoted an
upstream exception's text back to the user.

- app/refusal.py: `refused(status, reason, **params)` → {code: "refused",
  reason, …params}; localizeDetail translates errors.refused.<reason> with the
  params interpolated. "Unknown X" 404s use the existing not_found(what).
- sysconfig.set_value raises InvalidSetting (reason + bounds) instead of an
  English ValueError; the three writers answer it through setting_refused.
- The Plex connection/write/image failures log what the upstream said and
  answer a reason; the search scraper's failure is logged and answered as
  youtube/unavailable (it crashed refusal_reason before).
- HttpError.detail now only ever holds a translated reason: a string detail
  (only the framework's own can remain) is left out, so reading .detail is
  safe everywhere — including destructured, the hole the raw-detail source
  scan could not see. That scan and its five-file exception list are gone.
- Enforced: test_http_details.py fails on any HTTPException with a sentence
  for a detail; the contract test requires every refused reason and every
  not_found "what" in both languages, and no key for one that is gone.
- local/jsx-comment-text: a // inside JSX children renders as text; the rule
  is ten lines in eslint.config.js rather than eslint-plugin-react's ~1800
  lockfile lines.

frontend/src/i18n/locales/en/errors.json

@@ -21,7 +21,21 @@
     "job": "This job doesn't exist any more.",
     "download": "This download doesn't exist any more.",
     "link": "This share link doesn't exist any more.",
-    "notification": "This notification doesn't exist any more."
+    "notification": "This notification doesn't exist any more.",
+    "account": "That account no longer exists.",
+    "collection": "This collection doesn't exist any more.",
+    "config_key": "There's no such setting.",
+    "file": "The file is no longer available.",
+    "filmstrip": "There's no filmstrip for this.",
+    "host": "This host isn't on the list any more.",
+    "image": "There's no image for this.",
+    "item": "This item doesn't exist any more.",
+    "library": "This library doesn't exist any more.",
+    "plex_item": "This Plex item isn't in the library any more.",
+    "poster": "There's no poster for this.",
+    "profile": "This download profile doesn't exist any more.",
+    "season": "This season isn't in the library any more.",
+    "show": "This show isn't in the library any more."
   },
   "admin": {
     "not_allowed": "Their address isn't approved any more. Add it to the whitelist first.",
@@ -99,5 +113,98 @@
     "quota": "Today's YouTube budget for this instance is spent. It resets at midnight Pacific time — try again then.",
     "reconnect": "Google no longer accepts this account's YouTube connection. Sign out and sign in with Google again to reconnect it.",
     "unavailable": "YouTube didn't accept that just now. Please try again."
+  },
+  "refused": {
+    "account_no_access": "That account no longer has access.",
+    "account_signed_out": "That account was signed out elsewhere — sign in again.",
+    "account_suspended": "That account is suspended.",
+    "address_has_account": "That address already has an account — delete the account instead.",
+    "admin_first": "Create the admin account first.",
+    "admin_only": "Only an admin can do that.",
+    "already_set_up": "This instance is already set up.",
+    "already_subscribed": "You're already subscribed to this channel.",
+    "channel_blocked": "You've blocked this channel.",
+    "collection_fields_required": "A title and an item are both needed.",
+    "collection_pending_sync": "The collection changed in Plex, but refreshing the local copy failed — it catches up on the next sync.",
+    "collection_read_only": "This collection is read-only.",
+    "collection_smart": "Smart and auto-list collections can't be made editable.",
+    "demo_activate": "The demo account can't be activated.",
+    "demo_delete": "The demo account can't be deleted.",
+    "demo_role": "The demo account's role can't be changed.",
+    "demo_suspend": "The demo account can't be suspended.",
+    "download_not_ready": "This download isn't ready.",
+    "edit_unfinished": "Only a finished download can be edited.",
+    "filters_not_object": "The view's filters are malformed.",
+    "google_no_userinfo": "Google didn't send back the account details. Try signing in again.",
+    "image_fetch_failed": "The image couldn't be loaded.",
+    "image_host": "Images from that address aren't loaded.",
+    "invalid_cursor": "The list position is out of date — reload the page.",
+    "invalid_email": "Enter a valid email address.",
+    "invalid_interval": "The interval must be between {{min}} and {{max}} minutes.",
+    "invalid_link": "That doesn't look like a valid video link.",
+    "invalid_role": "Unknown role.",
+    "invalid_status": "Unknown status.",
+    "invite_decided": "This request has already been decided.",
+    "job_running": "This job is already running.",
+    "last_active_admin": "This is the only active admin — make someone else admin first.",
+    "last_admin": "This is the only admin — make someone else admin first.",
+    "link_gone": "This link is no longer available.",
+    "link_required": "A video link or id is required.",
+    "media_missing": "The media file isn't on disk.",
+    "message_empty": "The message is empty.",
+    "message_rate": "Too many messages — slow down a moment.",
+    "message_self": "You can't message yourself.",
+    "message_too_long": "The message is too long.",
+    "messaging_set_up": "Secure messaging is already set up.",
+    "name_required": "A name is required.",
+    "no_encryption_key": "Set TOKEN_ENCRYPTION_KEY to store secrets in the database.",
+    "no_messaging": "That member hasn't set up messaging yet.",
+    "no_profile": "There's no download profile to use.",
+    "no_subscription_id": "There's no YouTube subscription on record yet — sync your subscriptions first.",
+    "not_authenticated": "You're not signed in.",
+    "not_ready": "Not available yet.",
+    "not_redownloadable": "This item can't be downloaded again.",
+    "not_your_account": "That's not an account you've signed into here.",
+    "only_admin_delete": "You're the only admin — make someone else admin before deleting your account.",
+    "own_delete": "Delete your own account in Settings → Account.",
+    "own_role": "You can't change your own role.",
+    "own_suspend": "You can't suspend your own account.",
+    "plex_disabled": "The Plex module is turned off.",
+    "plex_not_configured": "Plex isn't set up — add the server address and token in Configuration → Plex.",
+    "plex_unreachable": "The Plex server didn't answer. Check the address and the token, then try again.",
+    "plex_write_failed": "Plex didn't accept the change. Try again.",
+    "profile_name_required": "A profile name is required.",
+    "quota_reserve": "Today's shared YouTube budget is down to its reserve — try again later.",
+    "quota_spent": "Today's shared YouTube budget is spent. Try again tomorrow.",
+    "recipient_required": "A recipient email is required.",
+    "registration_closed": "Registration is currently closed.",
+    "search_daily_limit": "You've reached today's YouTube search limit ({{limit}}). Try again tomorrow.",
+    "search_term_required": "Enter something to search for.",
+    "session_gone": "The playback session ended.",
+    "setting_not_a_choice": "Pick one of: {{choices}}.",
+    "setting_not_a_number": "Enter a whole number.",
+    "setting_too_high": "The value can be at most {{max}}.",
+    "setting_too_low": "The value must be at least {{min}}.",
+    "setup_token": "The setup token is missing or wrong.",
+    "share_own": "That's already your download.",
+    "share_password_required": "This link needs a password.",
+    "share_unfinished": "Only a finished download can be shared.",
+    "smtp_failed": "The email couldn't be sent — check the SMTP settings.",
+    "smtp_off": "SMTP isn't configured.",
+    "spec_not_object": "The profile's settings are malformed.",
+    "still_downloading": "This download is still in progress.",
+    "tag_name_taken": "You already have a tag named “{{name}}”.",
+    "title_required": "A title is required.",
+    "too_many_attempts": "Too many attempts. Try again shortly.",
+    "unknown_setting": "Unknown setting: {{key}}",
+    "value_missing": "A value is required.",
+    "video_gone": "This video is no longer available.",
+    "view_name_taken": "You already have a view named “{{name}}”.",
+    "watch_sync_off": "Turn on Plex watch-sync first.",
+    "weak_password": "The password must be at least {{min}} characters.",
+    "wrong_password": "The current password is incorrect.",
+    "wrong_share_password": "Wrong password.",
+    "youtube_editing_off": "Turn on YouTube editing in Settings first.",
+    "youtube_read_scope": "Connect your YouTube account (read access) first."
   }
 }