feat(ui): on-device move preview (local eval) with network fallback

Score and validate a tentative move on-device instead of a per-arrangement
network round trip. The dawg reader and the validate/score/direction slice of the
scrabble-solver engine are ported to TypeScript (ui/src/lib/dict), pinned
byte-for-byte to the Go engine by a new `conformance` CI job. The server stays
authoritative — submit_play re-validates — so the local result is an advisory
accelerator only; any cache miss, storage eviction or a bad-connection breaker
falls back to the network evaluate.

- backend: Registry.DictBytes + an authed GET /api/v1/user/dict/{variant}/{version}
  (immutable) streaming the pinned per-game dawg.
- gateway: a session-gated /dict edge route proxying it; fetchDict on the transport.
- client: an IndexedDB blob cache (best-effort, storage.persist()) + a loader
  (memory -> IndexedDB -> network, session-scoped bad-connection breaker) + a lobby
  prefetch (your-turn first); an adapter over the existing premiums/alphabet; a
  DictWarmup overlay while a cold dictionary loads (120ms flash-guard, 5s cap ->
  network); a ?nolocal flag; the DebugPanel reset also clears the dict cache.
- parity: generators backend/cmd/{dictgen,validategen} + gated Vitest suites, run
  in CI against the release dictionaries.
- docs: ARCHITECTURE §5, TESTING, UI_DESIGN, FUNCTIONAL (+ru).

.gitea/workflows/ci.yaml

@@ -207,11 +207,66 @@ jobs:
         run: pnpm run test:e2e
         timeout-minutes: 5
 
+  # conformance proves the client's local move preview (the ported dawg reader +
+  # validator, ui/src/lib/dict) byte-for-byte against the authoritative Go engine:
+  # a Go step generates golden parity vectors from the release dictionaries, then the
+  # gated Vitest suite replays them. It spans both toolchains, so it runs whenever the
+  # Go engine side or the UI side changed.
+  conformance:
+    needs: changes
+    if: ${{ needs.changes.outputs.go == 'true' || needs.changes.outputs.ui == 'true' }}
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: bash
+    env:
+      GOPRIVATE: gitea.iliadenisov.ru/*
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Fetch dictionary DAWGs
+        run: |
+          mkdir -p "${GITHUB_WORKSPACE}/dawg"
+          curl -fsSL -o /tmp/dawg.tar.gz "https://gitea.iliadenisov.ru/developer/scrabble-dictionary/releases/download/${DICT_VERSION}/scrabble-dawg-${DICT_VERSION}.tar.gz"
+          tar xzf /tmp/dawg.tar.gz -C "${GITHUB_WORKSPACE}/dawg"
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: go.work
+          cache: true
+
+      - name: Generate golden parity vectors
+        run: |
+          go run ./backend/cmd/dictgen -dawg-dir "${GITHUB_WORKSPACE}/dawg" -out /tmp/dictgold
+          go run ./backend/cmd/validategen -dawg-dir "${GITHUB_WORKSPACE}/dawg" -out /tmp/validgold
+
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+
+      - name: Install pnpm
+        run: npm install -g pnpm@11.0.9
+
+      - name: Install deps
+        working-directory: ui
+        run: pnpm install --frozen-lockfile
+
+      - name: Local-eval conformance (reader + validator vs the Go engine)
+        working-directory: ui
+        env:
+          DICT_DAWG_DIR: ${{ github.workspace }}/dawg
+          DICT_GOLD_DIR: /tmp/dictgold
+          DICT_VALID_DIR: /tmp/validgold
+        run: pnpm exec vitest run src/lib/dict/
+
   # gate is the single branch-protection required check. It always runs and passes
   # only when each upstream job succeeded or was skipped (a path-filtered no-op),
   # failing the merge if any actually failed or was cancelled.
   gate:
-    needs: [unit, integration, ui]
+    needs: [unit, integration, ui, conformance]
     if: always()
     runs-on: ubuntu-latest
     defaults:
@@ -221,7 +276,7 @@ jobs:
       - name: Aggregate required checks
         run: |
           fail=
-          for r in "unit:${{ needs.unit.result }}" "integration:${{ needs.integration.result }}" "ui:${{ needs.ui.result }}"; do
+          for r in "unit:${{ needs.unit.result }}" "integration:${{ needs.integration.result }}" "ui:${{ needs.ui.result }}" "conformance:${{ needs.conformance.result }}"; do
             name="${r%%:*}"; res="${r#*:}"
             echo "$name = $res"
             case "$res" in