test(offline): real-dictionary move-generator conformance in CI

Phase A (A4): prove the ported move generator (#188) against the FULL shipped
dictionaries, not just the tiny samples — the deep graphs and complete 26/33-letter
alphabets the samples cannot reach.

- backend/cmd/movegen: add a -dawg-dir mode that emits per-variant golden move-gen
  vectors from the real dawgs (a bounded first-move + a blank case + a deep 7-tile
  mid-game position). Regenerated in CI to /tmp, never committed (like the
  dictgen/validategen vectors), so no dictionary version is pinned into the repo.
- ui/src/lib/dict/generate.realparity.test.ts: env-gated (DICT_DAWG_DIR +
  DICT_MOVEGEN_DIR) parity against that golden — 9 positions across scrabble_en /
  scrabble_ru / erudit_ru match the Go solver exactly. Skips cleanly when unset.
- .gitea/workflows/ci.yaml: the conformance job now generates the movegen golden
  and points the gated vitest at it (DICT_MOVEGEN_DIR).

.gitea/workflows/ci.yaml

@@ -252,6 +252,7 @@ jobs:
         run: |
           go run ./backend/cmd/dictgen -dawg-dir "${GITHUB_WORKSPACE}/dawg" -out /tmp/dictgold
           go run ./backend/cmd/validategen -dawg-dir "${GITHUB_WORKSPACE}/dawg" -out /tmp/validgold
+          go run ./backend/cmd/movegen -dawg-dir "${GITHUB_WORKSPACE}/dawg" -out "${GITHUB_WORKSPACE}/movegold"
 
       - name: Set up Node
         uses: actions/setup-node@v4
@@ -271,6 +272,7 @@ jobs:
           DICT_DAWG_DIR: ${{ github.workspace }}/dawg
           DICT_GOLD_DIR: /tmp/dictgold
           DICT_VALID_DIR: /tmp/validgold
+          DICT_MOVEGEN_DIR: ${{ github.workspace }}/movegold
         run: pnpm exec vitest run src/lib/dict/
 
   # gate is the single branch-protection required check. It always runs and passes