Add Gitea Actions CI + switch to PR-based workflow

- Add .gitea/workflows/ci.yml: typecheck -> lint -> unit -> build -> deterministic
  Playwright e2e against the dev webServer (LLM_STUB=1). No dind/docker/static IP.
- package-lock.json is committed (reproducible `npm ci`); verified npm install is a no-op.
- Add CHANGELOG.md, set version 0.1.0, add .env (gitignored) + .env.example placeholder.
- Document the mandatory feature-branch -> PR -> CI -> auto-merge workflow in
  AGENTS.md + README.md (e2e now runs in CI on every PR).
- Add Playwright html/json reporters (playwright-report/, test-results/e2e.json)
  for the CI E2E-results summary step and the failure artifact upload.

playwright.config.ts

@@ -18,6 +18,13 @@ export default defineConfig({
     baseURL: devUrl,
     headless: true,
   },
+  // Reporters: list → console; html → playwright-report/ (uploaded by CI on failure);
+  // json → test-results/e2e.json (parsed by CI's "E2E results summary" step).
+  reporter: [
+    ['list'],
+    ['html'],
+    ['json', { outputFile: 'test-results/e2e.json' }],
+  ],
   webServer: {
     command: 'npm run dev',
     url: devUrl,