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/hu/inbox.json

@@ -30,8 +30,8 @@
     "titleError": "{{job}} hibázott"
   },
   "emailUndelivered": {
-    "title": "Egy e-mailt nem sikerült elküldeni",
-    "notConfigured": "Az SMTP nincs beállítva, ezért a(z) „{{subject}}” kimaradt. Amíg nincs beállítva, egyetlen üzenet sem hagyja el ezt a példányt.",
-    "sendFailed": "A levelezőszerver visszautasította a(z) „{{subject}}” üzenetet. Nézd meg a Konfiguráció → E-mail / SMTP fület, és küldj tesztet."
+    "title": "Nem megy ki e-mail",
+    "notConfigured": "Az SMTP nincs beállítva, így semmi nem kézbesíthető, amit ez a példány küldene — megerősítő linkek, jelszó-visszaállítások és hozzáférés-kérelmek egyaránt. A legutóbbi: „{{subject}}”.",
+    "sendFailed": "A levelezőszerver visszautasított egy üzenetet, tehát a kézbesítés hibára fut — a legutóbbi: „{{subject}}”. Nézd meg a Konfiguráció → E-mail / SMTP fület, és küldj tesztet."
   }
 }