chore: initial repository scaffolding

- Add README with features, quick-start (local + Docker) and docs index
- Add MIT LICENSE, root .gitignore and .env.example
- Add docker-compose.yml (postgres + backend + frontend)
- Add root package.json with install:all/dev helpers
- Add Gitea CI workflow (backend syntax check, frontend build)

.gitea/workflows/ci.yml

@@ -0,0 +1,25 @@
+name: ci
+on: [push, pull_request]
+jobs:
+  backend:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+      - run: npm ci
+        working-directory: backend
+      - run: node --check src/index.js && node --check src/socket.js
+        working-directory: backend
+  frontend:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+      - run: npm ci
+        working-directory: frontend
+      - run: npm run build
+        working-directory: frontend