fix(gmail): stop hiding why it failed, twice over

Reported from use: "Fetch now" said "something went wrong" and the error log was
empty. Both halves were the same bug wearing two hats.

`handleGmailSyncNow` answered 502 with the code `internal_error`, which the
interface maps to a generic sentence — so Google's own words, which are the whole
diagnosis, were replaced by one that says nothing. And `writeError` records
nothing; only `s.internal` does. So there was no message to read and nowhere to
look it up afterwards.

`s.upstream()` is the answer: 502 because this is somebody else's service saying
no rather than this server breaking, a code of its own so the interface can quote
what was said, and a row in the error log — which is the entire reason that log
exists. A Gmail sync failing quietly for a week is otherwise invisible: the
background job writes a line the next restart erases.

The same connection also left the mailbox unnamed. The address is learned at
connect time and that call can fail; a warning went to the log and an empty string
to the database, so the page said "an unknown account" and kept saying it. The only
way back was to disconnect and reconnect, which nobody would guess. The status
endpoint asks again when it finds none, so a wrong answer lasts until the next look
rather than until somebody reconnects.

Ten Danish strings were hiding in `confirm()` and `app.toast()` calls, including
every destructive confirmation in the app — the worst possible set to leave in one
language, since it is what somebody reads in the half-second before agreeing to
lose something. The i18n guard reads markup and attributes, and a string argument
lives in the script block. It reads those now, and found four my own grep missed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/src/lib/api.js

@@ -55,6 +55,9 @@ const MESSAGES = {
 	ai_not_configured: 'error.aiNotConfigured',
 	totp_not_enabled: 'error.totpNotEnabled',
 	inbox_protected: 'error.inboxProtected',
+	// The fallback for when Gmail refused and said nothing usable. When it did say
+	// something, `humanMessage` quotes it instead — see below.
+	gmail_failed: 'error.gmailRefused',
 	last_admin: 'error.lastAdmin'
 };
 
@@ -67,6 +70,15 @@ const MESSAGES = {
  */
 export function humanMessage(err) {
 	if (!(err instanceof ApiError)) return t(MESSAGES.offline);
+
+	// Gmail's own words are the diagnosis — "invalid_grant", "insufficient
+	// authentication scopes" — and a generic sentence in their place throws away
+	// the only thing that says what to do. Wrapped so it reads as a quotation
+	// rather than as a stray English string in a Danish interface.
+	if (err.code === 'gmail_failed' && err.message) {
+		return t('error.gmailSaid', { what: err.message });
+	}
+
 	const key = MESSAGES[err.code];
 	if (key) return t(key);
 	return err.message ?? t(MESSAGES.internal_error);