feat: Add allow_local_network option for self-hosted LLM proxies

Add per-instance boolean option to allow private IP endpoints and HTTP
scheme for self-hosted LLM proxies (LiteLLM, Ollama, vLLM, etc.).

- New CONF_ALLOW_LOCAL_NETWORK config option (default: false)
- When enabled: allows RFC1918 private IPs and HTTP endpoints
- When disabled: full SSRF protection preserved (HTTPS + public IPs only)
- Multicast and unspecified addresses blocked regardless of setting
- Warning logged when local network mode is active
- Checkbox added to ConfigFlow and OptionsFlow UI
- Translations for all 8 languages

Closes #9

custom_components/ha_text_ai/manifest.json

@@ -15,5 +15,5 @@
     "google-genai>=1.16.0"
   ],
   "single_config_entry": false,
-  "version": "2.4.0"
+  "version": "2.4.1"
 }