ci: enable ruff linting and pytest in CI pipeline

Uncomment the ruff check and pytest steps in the Gitea Actions build
workflow so that linting violations and test failures block image builds.
Fix all pre-existing ruff violations (E402 import ordering in analyzer.py,
F821 undefined name in api.py, I001 unsorted imports in test files, F401
unused import in test_rate_limit.py).

Closes leeworks-agents/SPARC#1559
Closes leeworks-agents/SPARC#1560

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build.yaml

@@ -28,10 +28,10 @@ jobs:
         run: |
           pip3 install -r requirements.txt ruff
 
-#      - name: Run ruff linter
-#        shell: sh
-#        run: |
-#          ruff check SPARC/ tests/
+      - name: Run ruff linter
+        shell: sh
+        run: |
+          ruff check SPARC/ tests/
 
       - name: Install Node.js and check TypeScript types
         shell: sh
@@ -47,16 +47,17 @@ jobs:
           fi
           npx tsc --noEmit
 
-#      - name: Run pytest
-#        shell: sh
-#        env:
-#          DATABASE_URL: "sqlite://"
-#          API_KEY: "test-key"
-#          OPENROUTER_API_KEY: "test-key"
-#          JWT_SECRET: "test-secret-for-ci"
-#          APP_ENV: "development"
-#        run: |
-#          python3 -m pytest tests/ -v --tb=short -x
+      - name: Run pytest
+        shell: sh
+        env:
+          DATABASE_URL: "sqlite://"
+          API_KEY: "test-key"
+          OPENROUTER_API_KEY: "test-key"
+          JWT_SECRET: "test-secret-for-ci"
+          APP_ENV: "development"
+        run: |
+          pip3 install pytest
+          python3 -m pytest tests/ -v --tb=short -x
 
   build-api:
     needs: test