Report question: skip a broken card and tell the server

A generated matching card arrived on a phone with three identical
definitions (the generation guards now drop those), but there was no way
to get past a bad card from inside a session. The feed chrome (deck
study, review, mistakes and exam) now has the red "!" control: one tap
records the question, skips to the next card and shows an Undo toast.

- lib/question-reports.ts: the local list (freezmo.reports.v1, zod on
  read, capped 200) is the skip state — reported cards leave every
  session type, count as "not attempted" in the results instead of
  wrong, and Undo takes a report back. A deck where everything is
  reported stays studiable so it can be regenerated.
- POST /api/reports appends one JSON line per report to
  REPORTS_DIR/reports.jsonl (shared/freezmo/reports in production, the
  dev data dir in dev). Deliberately write-only: the question text is
  readable on the server (that is the point — prompt tuning) but never
  over HTTP, since the app has no auth. Best effort: offline reports stay
  local.
- The button: a red outlined rounded square with "!", the chrome's
  control size, in both feed headers (hidden on the results slide).
- config: REPORTS_DIR + RATE_LIMIT_REPORTS (20); the deploy creates the
  shared reports dir; the dev unit and AGENTS.md note the new server
  data location.
- Suites: phase-1 (append + validation + no GET), phase-2 (button, toast,
  server POST, local copy, skip counter, hidden next session, Undo, exam
  pool). SW -> freezmo-v38.

AGENTS.md

@@ -41,7 +41,7 @@ Production only ever runs a pushed, verified commit deployed by
 5. **The Ollama API key never leaves the browser.** It must never appear in
    exports, sync payloads, share links, logs, URLs, `.env` files committed to
    the repo, or release directories. Server data (sync blobs, push
-   subscriptions) lives only under `shared/`.
+   subscriptions, question reports) lives only under `shared/`.
 6. **Both languages, always.** Every user-facing string goes into
    `lib/i18n-dict.ts` in **en and cs** (the i18n test enforces key parity).
 7. **Phones are first-class**: ≤639px layouts, 44px touch targets, 16px