Fix AttributeError in OptionsFlow and add loading icon overlay

- Fix BomLocalOptionsFlow AttributeError by using super().__init__() instead of direct assignment
- Add single_config_entry to manifest to enforce single integration instance
- Add YAML config check to prevent UI config when YAML config exists
- Add icon static path registration for /local/community/bom_local/icon.png
- Add loading overlay with animated icon to card
- Bump version to 0.3.0

Fixes #1

custom_components/bom_local/manifest.json

@@ -3,8 +3,9 @@
   "name": "BOM Local Radar",
   "codeowners": ["@alexhopeoconnor"],
   "config_flow": true,
+  "single_config_entry": true,
   "iot_class": "local_polling",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "dependencies": ["http", "websocket_api"],
   "documentation": "https://github.com/alexhopeoconnor/bom-local-card",
   "issue_tracker": "https://github.com/alexhopeoconnor/bom-local-card/issues"