feat: comprehensive code review fixes + receivers-only architecture

Security:
- Refuse startup with default secret_key in production (was just logging)
- Settings endpoint now requires admin role
- Password validation on initial setup
- DOM-based HTML sanitizer replaces regex in template previews
- Add *.log to .gitignore

Performance & reliability:
- Token refresh deduplication prevents race condition on concurrent 401s
- Theme media query listener registered once (no leak)
- IconPicker uses $derived instead of function call per render
- Snackbar uses single-batch state update instead of while loop
- Replace 11 inline hover handlers with CSS :hover in layout

Architecture - receivers-only:
- Delivery endpoints (chat_id, email, url, room_id, topic) now stored
  exclusively in TargetReceiver rows, never in target.config
- Migration extracts existing delivery fields to receiver rows
- Notifier and dispatcher remove all config fallbacks
- Frontend targets page shows receivers list per target with
  add/remove/toggle/test per receiver
- Single-receiver test endpoint: POST /targets/{id}/receivers/{id}/test

Code quality:
- Extract AuthLayout.svelte from login/setup (150 lines CSS dedup)
- Split telegram-bots page (754→51 lines + 3 tab components)
- Split notification-trackers page (547→432 lines + 4 components)
- Deduplicate _send_reply into shared handler.send_reply()
- Add locale column to template models, replace name-based detection
- Fix delete_notification_tracker dead protection check
- Fix check_telegram_bot query (filter by type, remove bogus OR)
- Add graceful scheduler shutdown in lifespan
- Consistent /bots?tab=telegram URLs across all nav links

i18n:
- Error page, chat actions, target types, provider types internationalized
- All new receiver UI strings in EN + RU

packages/server/src/notify_bridge_server/services/telegram_poller.py

@@ -180,7 +180,7 @@ async def _poll_bot(bot_id: int) -> None:
     _last_update_id[bot_id] = updates[-1]["update_id"]
 
     # Process each update
-    from ..commands.handler import handle_command, send_media_group
+    from ..commands.handler import handle_command, send_media_group, send_reply
 
     for update in updates:
         message = update.get("message")
@@ -210,22 +210,8 @@ async def _poll_bot(bot_id: int) -> None:
                     if isinstance(cmd_response, list):
                         await send_media_group(bot_token, chat_id, cmd_response)
                     else:
-                        await _send_reply(bot_token, chat_id, cmd_response)
+                        await send_reply(bot_token, chat_id, cmd_response)
             except Exception:
                 _LOGGER.error("Error handling command from bot %d", bot_id, exc_info=True)
 
 
-async def _send_reply(bot_token: str, chat_id: str, text: str) -> None:
-    """Send a text reply via Telegram Bot API."""
-    async with aiohttp.ClientSession() as http:
-        url = f"{TELEGRAM_API_BASE_URL}{bot_token}/sendMessage"
-        payload: dict[str, Any] = {"chat_id": chat_id, "text": text, "parse_mode": "HTML"}
-        try:
-            async with http.post(url, json=payload) as resp:
-                if resp.status != 200:
-                    result = await resp.json()
-                    if "parse" in str(result.get("description", "")).lower():
-                        payload.pop("parse_mode", None)
-                        await http.post(url, json=payload)
-        except aiohttp.ClientError as err:
-            _LOGGER.error("Failed to send Telegram reply: %s", err)