fix: Comprehensive v2.4.0 security, stability, and quality improvements

Security:
- Add SSRF protection via HTTPS-only endpoint validation with private IP blocking
- Mask API keys in all log output via safe_log_data()
- Sanitize error responses to prevent internal detail leakage
- Remove API key pre-population in config flow forms
- Harden service schemas with input length limits and type coercion

Bug fixes:
- Fix temperature=0 rejected due to Python falsy value bug (0 or default)
- Fix fire-and-forget race condition in coordinator init (5 async_create_task → awaited async_initialize)
- Fix rate limit state not resetting after successful API calls
- Fix ConnectionError incorrectly setting is_rate_limited=True
- Fix _rotate_history calling async method via sync executor
- Fix shutil.move blocking event loop in history migration
- Fix async_shutdown removing wrong key from hass.data
- Replace os.rename with shutil.move for cross-device safety

Improvements:
- Add asyncio.Lock for request serialization
- Replace async_timeout with stdlib asyncio.timeout (Python 3.12+)
- Use SupportsResponse.OPTIONAL for ask_question and get_history services
- Use Platform.SENSOR enum instead of string literal
- Add strings.json for HA translation framework
- Update DEFAULT_ANTHROPIC_MODEL to claude-sonnet-4-6
- Retry only transient errors (429, timeout) in API client

Cleanup:
- Remove dead code: unused schemas, imports, sync_write_history, check_memory, check_connection
- Remove icon copying code from async_setup
- Remove unused dependencies from manifest (anthropic, openai, certifi, async-timeout)
- Remove empty manifest arrays (bluetooth, mqtt, ssdp, usb, zeroconf)
- Fix duplicate JSON keys in 5 translation files
- Fix Serbian translation: "Прекључено" → "Искључено" for disconnected state

Bump version to 2.4.0

custom_components/ha_text_ai/manifest.json

@@ -2,7 +2,6 @@
   "domain": "ha_text_ai",
   "name": "HA Text AI",
   "after_dependencies": ["http"],
-  "bluetooth": [],
   "codeowners": ["@smkrv"],
   "config_flow": true,
   "dependencies": [],
@@ -11,20 +10,10 @@
   "iot_class": "cloud_polling",
   "issue_tracker": "https://github.com/smkrv/ha-text-ai/issues",
   "loggers": ["custom_components.ha_text_ai"],
-  "mqtt": [],
-  "quality_scale": "silver",
   "requirements": [
     "aiofiles>=23.0.0",
-    "aiohttp>=3.8.0",
-    "anthropic>=0.8.0",
-    "async-timeout>=4.0.0",
-    "certifi>=2024.2.2",
-    "google-genai>=1.16.0",
-    "openai>=1.12.0"
+    "aiohttp>=3.8.0"
   ],
   "single_config_entry": false,
-  "ssdp": [],
-  "usb": [],
-  "version": "2.3.0",
-  "zeroconf": []
+  "version": "2.4.0"
 }