fix(api): a write that hit a connection failure is still reported, and every failure is reported once

Deep-review round 4, the "one report per failure" contract round 3 introduced.

- `req` marked gateway (502/503/504) and network failures "already reported" because they raise
  the connection notice. But that notice is about connectivity and removes itself on the very next
  answer — which every caller's own resync refetch fetches at once — so a delete that hit a
  keepalive reset flashed the notice and was then reported nowhere, the list still there. Only the
  durable reports (the error dialog, the 401 sign-out) count now; the caller says the action failed.
- A connection notice the user closed swallowed every later one for the rest of the visit; it is
  raised again.
- `req` and `uploadReq` share one failure policy (`reportFailure`). The upload copy had drifted: a
  502 opened the blocking "Server error (502)" dialog and cleared a notice that was still true.
- A taken Plex collection name is a structured 409, localized, and the create/rename calls are
  quiet: it was an English dialog plus a Hungarian toast. `notifyCollectionEditError` is gone.
- The mutation onErrors that toasted unconditionally after a non-quiet request (invite approve /
  deny / add, demo whitelist, audit clear, scheduler, share, full history, edit, config tests, tag
  attach) go through `notifyActionError`; the playlist delete's hand-rolled copy of it too (it takes
  a level now). The user role / suspend / delete actions had no onError at all: a user deleted in
  another tab failed silently and stayed listed — now said, and the list refetched.

frontend/src/components/AuditLog.tsx

@@ -12,6 +12,7 @@ import { useConfirm } from "./ConfirmProvider";
 import DataTable from "./ui/DataTable";
 import { LoadingState, StateMessage } from "./ui/QueryState";
 import { auditColumns } from "./auditColumns";
+import { notifyActionError } from "../lib/actionErrors";
 
 // Admin-only audit trail: an append-only who/what/when log of admin actions + scheduler run
 // summaries (never per-row). Read-only apart from Clear. Client-side sort/filter/paginate via
@@ -36,7 +37,7 @@ export default function AuditLog() {
       qc.invalidateQueries({ queryKey: qk.adminAudit() });
       notify({ level: "success", message: t("audit.cleared", { count: r.cleared }) });
     },
-    onError: () => notify({ level: "error", message: t("audit.clearFailed") }),
+    onError: (e) => notifyActionError(e, t("audit.clearFailed")),
   });
   const onClear = async () => {
     if (