test(chat,playout): enable test suite, coverage gate, switch to pure-Go SQLite driver

.gitea/workflows/ci.yml

@@ -43,7 +43,17 @@ jobs:
         run: cd backend/chat && GOTOOLCHAIN=local go vet ./...
 
       - name: Run Tests
-        run: echo "Tests will be added in future CI steps"
+        run: cd backend/chat && GOTOOLCHAIN=local go test ./... -v -cover -coverprofile=coverage.out -race
+
+      - name: Check Coverage
+        run: |
+          cd backend/chat
+          COVERAGE=$(GOTOOLCHAIN=local go tool cover -func=coverage.out | grep total | awk '{print $3}' | sed 's/%//')
+          echo "Coverage: $COVERAGE%"
+          if [ "$(echo "$COVERAGE < 50" | bc)" -eq 1 ]; then
+            echo "Coverage $COVERAGE% below 50% threshold"
+            exit 1
+          fi
 
   docker:
     needs: test