fix: chat build syntax errors, disable GitHub cache on Gitea runner

- Fix 3 orphaned function bodies in main.go (handleAdminSchedule,
  handleAdminSystemSummary, probeMediaDurationSeconds) caused by
  insertions that split function headers from bodies
- Remove cache: true from setup-go and cache: npm from setup-node
  (Gitea runner times out 135s trying to reach GitHub cache API)
- Add go vet ./... step replacing placeholder echo
- Remove || echo fallback from lint (tsc --noEmit is working)

.gitea/workflows/ci.yml

@@ -19,14 +19,12 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: "20"
-          cache: "npm"
-          cache-dependency-path: frontend/package-lock.json
 
       - name: Install Frontend Dependencies
         run: cd frontend && npm ci
 
       - name: Lint Frontend
-        run: cd frontend && npm run lint || echo "Linting not configured yet"
+        run: cd frontend && npm run lint
 
       - name: Build Frontend
         run: cd frontend && npm run build
@@ -35,14 +33,15 @@ jobs:
         uses: actions/setup-go@v5
         with:
           go-version: "1.25"
-          cache: true
-          cache-dependency-path: backend/chat/go.sum
         env:
           GOTOOLCHAIN: local
 
       - name: Download Go modules
         run: cd backend/chat && GOTOOLCHAIN=local go mod download
 
+      - name: Validate Go
+        run: cd backend/chat && GOTOOLCHAIN=local go vet ./...
+
       - name: Run Tests
         run: echo "Tests will be added in future CI steps (per TODO.md)"