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

.dockerignore

@@ -0,0 +1,9 @@
+.git
+.gitignore
+.DS_Store
+*.swp
+data
+assets/preview.png
+assets/.DS_Store
+src/.DS_Store
+.version.json.swp