feat: runtime and UX polish

P1 features:
- System prompt injection on session resume (ThreadRecord gains system_prompt
  field, ensure_engine_loaded passes it to Op::SyncSession)
- Session resume bridge: GET/POST /v1/sessions/{id}, seed_thread_from_messages
- Task detail panel with deep links (?task=<id>), timeline, tool calls
- Tauri desktop build fix (CI=true in tauri:build script)

P2 features:
- Task detail auto-refresh polling for running/queued tasks (3s interval)
- Session delete: DELETE /v1/sessions/{id} endpoint + palette delete button
- Transcript full-text search input with combined role filter + search
- Per-item copy-to-clipboard, collapse/expand for long outputs, filter chips

Polish:
- Typography scale CSS variables, skeleton loading utilities
- Panel slide-in animation for task detail, fade-up for list items
- Toast auto-dismiss (4s success, 6s error) with dismiss buttons
- Focus trap in command palette, backdrop click to close
- Escape key closes task detail panel
- ARIA improvements: role=alert on error toasts, role=listbox on palette
- Responsive breakpoints for tablet (task detail stacking, palette width)
- prefers-reduced-motion respected throughout

All validation checks pass:
- cargo test (517 tests), cargo check
- pnpm typecheck, lint (0 errors), test (36 tests)
- pnpm web:build, desktop:build

.github/workflows/ci.yml

@@ -65,3 +65,24 @@ jobs:
         run: cargo doc --no-deps
         env:
           RUSTDOCFLAGS: -Dwarnings
+
+  frontend:
+    name: Frontend (deepseek-app)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 10.23.0
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: pnpm
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+      - name: Lint
+        run: pnpm deepseek-app:lint
+      - name: Typecheck
+        run: pnpm deepseek-app:typecheck
+      - name: Test
+        run: pnpm deepseek-app:test