feat: locale-aware notification templates + UX improvements

- Add locale support to notification templates (matching command template
  pattern): TemplateSlot now has locale field with (config_id, slot_name,
  locale) uniqueness, nested API format {slot: {locale: template}}
- Migration merges separate EN/RU system configs into unified per-provider
  configs; seeds create one config per provider with multi-locale slots
- Locale-aware dispatch with EN fallback in NotificationDispatcher
- Frontend locale tabs (EN/RU) on template config editor
- Fix tracking config cards not showing default provider icons
- Global provider filter, search palette, and various UX polish

frontend/src/lib/i18n/en.json

@@ -335,6 +335,11 @@
 		"clickToCopy": "Click to copy chat ID",
 		"chatsDiscovered": "Chats discovered",
 		"chatDeleted": "Chat removed",
+		"chatName": "Name",
+		"chatType": "Type",
+		"chatLang": "Lang",
+		"chatId": "Chat ID",
+		"languageUpdated": "Chat language updated",
 		"cmdLocale": "Bot language",
 		"searchCooldown": "Search cooldown (s)",
 		"saveConfig": "Save config",