feat: chat language display, disabled EntitySelect items, dev scripts

Chat language:
- Added language_code field to TelegramChat model + migration
- Saved from message.from.language_code on webhook/polling
- Displayed as badge on bot chat cards and target receiver items
- Resolved from DB in target API response (works for existing receivers)
- Shown in chat picker dropdown (desc includes language)

EntitySelect improvements:
- Tracker-target link selector shows all targets, already-linked ones
  appear disabled with "Already linked" hint
- Receiver chat picker shows already-added chats as disabled

Dev scripts:
- scripts/restart-backend.sh and restart-frontend.sh
- Updated .claude/docs/dev-servers.md to reference scripts

packages/server/src/notify_bridge_server/database/models.py

@@ -95,6 +95,7 @@ class TelegramChat(SQLModel, table=True):
     title: str = Field(default="")
     chat_type: str = Field(default="private")
     username: str = Field(default="")
+    language_code: str = Field(default="")
     discovered_at: datetime = Field(default_factory=_utcnow)