chore: beta release v0.5.0-beta

- Bump version to 0.5.0-beta
- Add Apache-2.0 LICENSE (official text) + NOTICE
- Add Docker support: multi-stage Dockerfile + docker-compose
  * non-root user, tini PID 1, gunicorn + uvicorn workers
  * healthcheck, OCI labels, persistent /data volume
- Add GitHub Actions CI (lint/import-check + Docker smoke-test)
- Backend polish:
  * modern lifespan handler (replaces deprecated on_event)
  * explicit sort validation (400 instead of 500)
  * title min_length=1 schema validation
  * configurable data dir + http timeout via env
  * avg_rating helper extracted (DRY)
- Frontend polish:
  * beta badge in title, footer with live version
  * loading spinner on initial fetch
  * updated README, badges, config table, roadmap

.github/workflows/ci.yml

@@ -0,0 +1,39 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+          cache: pip
+      - run: pip install -r requirements.txt
+      - name: Backend-Import-Check
+        run: |
+          python -c "from app.main import app; print('OK', app.title, app.version)"
+      - name: Frontend-Asset-Check
+        run: |
+          test -f app/static/index.html
+          test -f app/static/css/style.css
+          test -f app/static/js/app.js
+
+  docker:
+    runs-on: ubuntu-latest
+    needs: test
+    steps:
+      - uses: actions/checkout@v4
+      - name: Docker-Build
+        run: docker build -t watchstack:ci .
+      - name: Smoke-Test
+        run: |
+          docker run -d --rm --name ws -p 8765:8000 watchstack:ci
+          sleep 4
+          curl -fsS http://127.0.0.1:8765/api/health
+          docker stop ws