fix: address the feature review — accurate copy, reachable controls, real coverage

Round 1 on the feature diff found 15; the substantive ones:

- The delete control VANISHED on any invite whose address had registered, which
  is the ordinary sign-up shape (register writes the User and the pending invite
  together). The guard stays broad — that row is the account's approval gate, and
  orphaning it strands someone who can then neither sign in nor be approved — but
  the control is now a disabled button carrying the reason, on both lists, so an
  admin never sees a row silently missing a button its neighbours have.
- Deleting an entry is not always a revoke: is_allowed falls back to the env
  ALLOWED_EMAILS / ADMIN_EMAILS lists once no row exists, and an ADMIN_EMAILS
  address is force-promoted on its next Google sign-in. The route now reports
  still_allowed_by_env and the UI says so instead of claiming access was removed.
- "Deny keeps the row so they can't immediately re-ask" was simply false —
  upsert_pending_invite reopens a denied row. Corrected everywhere it was stated.
- The Configuration warning reads me.email_configured, which save() did not
  invalidate, so it kept warning about fields the admin had just filled in.
- The read-only variant was an aria-hidden span explained only by a Tooltip that
  the hints toggle can switch off; now a disabled button with title + aria-label.
- The delete error path threw away the 409's reason (the stale-list case) and
  left the stale row on screen.
- The throttle window was spent even when no notice was written, silencing the
  next hour on the path whose job is to stop silent drops.
- email_enabled() opened a second session and decrypted the SMTP password on
  every /api/me poll; it now takes the caller's session.
- welcomeMode.dom.test.ts never rendered the card, so reverting the history
  wiring to useState left it green. A render test now drives the real links and
  fails on that revert (verified).

Plus /api/me flag tests, the registration-shaped pending case, the env-allowlist
case, and a release note that matches what the code does.

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

@@ -167,12 +167,13 @@
     "denyConfirm": "Deny the access request from {{email}}?",
     "delete": "Delete",
     "deleteLabel": "Delete {{email}} from the whitelist",
-    "deleteHint": "Remove this address entirely. A later request from it starts over.",
+    "deleteHint": "Forget this address. A later request from it comes back as a new one.",
     "deleteTitle": "Delete whitelist entry?",
-    "deleteConfirm": "Remove {{email}} from the whitelist? If they were approved, they lose access until you add them again.",
-    "deleteHasAccount": "This address has an account — delete the user instead.",
+    "deleteConfirm": "Forget {{email}}? Siftlode drops the record, including an approval you already gave, so anyone at that address would have to ask again.",
+    "deleteHasAccount": "Someone has registered on this address — manage it under Users & roles, where deleting the account removes this entry too.",
     "deleted": "Whitelist entry removed.",
     "deleteFailed": "Could not remove the entry.",
-    "emailOff": "Email sending is not configured, so nobody gets a verification link and you get no notice when someone signs up. Fix it under Configuration → Email / SMTP."
+    "emailOff": "Email sending is not configured, so nobody gets a verification link and you get no notice when someone signs up. Fix it under Configuration → Email / SMTP.",
+    "deletedStillAllowed": "Entry removed, but this address is still allow-listed by the server's configuration, so it keeps access. Remove it from ALLOWED_EMAILS / ADMIN_EMAILS to change that."
   }
 }