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

frontend/src/lib/i18n/en.json

@@ -105,6 +105,7 @@
 		"online": "Online",
 		"offline": "Offline",
 		"checking": "Checking...",
+		"typeImmich": "Immich",
 		"loadError": "Failed to load providers.",
 		"externalDomain": "External Domain",
 		"optional": "optional",
@@ -228,6 +229,14 @@
 		"sendLargeAsDocuments": "Send large photos as documents",
 		"chatAction": "Chat action",
 		"chatActionNone": "None (no action)",
+		"chatActionTyping": "Typing",
+		"chatActionUploadPhoto": "Upload Photo",
+		"chatActionUploadVideo": "Upload Video",
+		"chatActionUploadDoc": "Upload Doc",
+		"chatActionRecordVideo": "Record Video",
+		"chatActionRecordVoice": "Record Voice",
+		"typeTelegram": "Telegram",
+		"typeWebhook": "Webhook",
 		"overrideUsername": "Override bot username",
 		"ntfyServer": "ntfy Server URL",
 		"ntfyTopic": "Topic",
@@ -236,7 +245,16 @@
 		"selectEmailBot": "Select Email Bot",
 		"selectMatrixBot": "Select Matrix Bot",
 		"recipientEmail": "Recipient Email",
-		"matrixRoomId": "Room ID"
+		"matrixRoomId": "Room ID",
+		"receivers": "Receivers",
+		"noReceivers": "No receivers yet",
+		"addReceiver": "Add Receiver",
+		"receiverAdded": "Receiver added",
+		"receiverDeleted": "Receiver deleted",
+		"receiverUpdated": "Receiver updated",
+		"confirmDeleteReceiver": "Delete this receiver?",
+		"receiverEnabled": "Receiver enabled",
+		"receiverDisabled": "Receiver disabled"
 	},
 	"users": {
 		"title": "Users",
@@ -702,6 +720,10 @@
 		"line": "line",
 		"add": "Add"
 	},
+	"error": {
+		"notFound": "Page not found",
+		"goHome": "Go home"
+	},
 	"searchPalette": {
 		"placeholder": "Search entities...",
 		"noResults": "No results found",