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>

internal/httpapi/auth_handlers.go

@@ -573,6 +573,34 @@ func inboxName(locale string) string {
 // 11:49" long after the line explaining it has gone, which tells an operator that
 // something broke and gives them no way to find out what. The row outlives the
 // container; Indstillinger → Fejl is where it is read.
+// upstream reports a failure that came from somebody else's service.
+//
+// Separate from `internal` because the cause is different and so is the fix: a 500
+// is this server broken, and this is Google — or whoever — saying no. The status
+// says so (502), and the message is passed through rather than replaced, because
+// "invalid_grant" or "insufficient authentication scopes" is the whole diagnosis
+// and a generic sentence in its place throws it away.
+//
+// It is recorded like a 500 for exactly the reason the error log exists: a Gmail
+// sync that has been failing for a week is invisible otherwise. The background job
+// writes a log line the next restart erases, and nobody is watching the one screen
+// that would have said so.
+func (s *Server) upstream(w http.ResponseWriter, r *http.Request, code, what string, err error) {
+	s.log.Warn(what, "err", err)
+
+	userID := ""
+	if u := userFrom(r.Context()); u != nil {
+		userID = u.ID
+	}
+	s.db.RecordError(r.Context(), store.ServerError{
+		Method: r.Method, Path: r.URL.Path, Status: http.StatusBadGateway,
+		What: what, Message: err.Error(), UserID: userID,
+		RequestID: middleware.GetReqID(r.Context()),
+	})
+
+	writeError(w, http.StatusBadGateway, code, err.Error())
+}
+
 func (s *Server) internal(w http.ResponseWriter, r *http.Request, what string, err error) {
 	s.log.Error(what, "err", err)