ci: add Gitea Actions workflow for automated testing

- Create .gitea/workflows/ci.yml with 4 sequential jobs
  - lint: Run ESLint on root configuration
  - test-backend: Run backend Vitest tests with SQLite
  - test-frontend: Run frontend Vitest tests
  - test-e2e: Run Playwright E2E tests (bloqueante)
- E2E job automates server startup + Playwright test execution
- Configure Gitea Secrets for IGDB, RAWG, TheGamesDB API keys
- Add artifact upload for Playwright reports on failure
- Update SECURITY.md with CI/CD Secrets setup instructions
- Update docs/API_KEYS.md with production Gitea workflow guide
- Add tests/gitea-workflow.spec.ts with 12 validation tests
- Workflow triggers on push/PR to main and develop branches

yarn.lock

@@ -5465,6 +5465,7 @@ __metadata:
     prettier: "npm:^3.8.1"
     typescript: "npm:^5.9.3"
     vitest: "npm:^0.34.1"
+    yaml: "npm:^2.8.2"
   languageName: unknown
   linkType: soft
 
@@ -7119,6 +7120,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"yaml@npm:^2.8.2":
+  version: 2.8.2
+  resolution: "yaml@npm:2.8.2"
+  bin:
+    yaml: bin.mjs
+  checksum: 10c0/703e4dc1e34b324aa66876d63618dcacb9ed49f7e7fe9b70f1e703645be8d640f68ab84f12b86df8ac960bac37acf5513e115de7c970940617ce0343c8c9cd96
+  languageName: node
+  linkType: hard
+
 "yn@npm:3.1.1":
   version: 3.1.1
   resolution: "yn@npm:3.1.1"