Harden Docker packaging and bundle frontend assets locally

- replace fragile Docker file bind mount with persistent /data storage
- add container entrypoint to link config.json from persistent storage
- tighten Docker image permissions and add a basic healthcheck
- add .dockerignore to keep git metadata and runtime files out of the image
- bundle hls.js locally instead of loading it from a CDN
- download and serve UI/theme fonts locally instead of Google Fonts
- update service worker cache entries for local assets
- refresh README to reflect local bundled assets and cleaner deployment docs

src/tpl/footer.php

@@ -1,4 +1,4 @@
-<script src="https://cdnjs.cloudflare.com/ajax/libs/hls.js/1.4.12/hls.min.js"></script>
+<script src="/assets/vendor/hls.min.js"></script>
 <script>
 <?php
 $js_dir = __DIR__ . '/../js/';