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

frontend/src/routes/bots/TelegramBotTab.svelte

@@ -306,6 +306,7 @@
 										<div class="flex items-center gap-2">
 											<span class="font-medium">{chat.title || chat.username || 'Unknown'}</span>
 											<span class="text-xs px-1.5 py-0.5 rounded bg-[var(--color-muted)] text-[var(--color-muted-foreground)]">{chatTypeLabel(chat.type)}</span>
+											{#if chat.language_code}<span class="text-xs px-1.5 py-0.5 rounded bg-[var(--color-muted)] text-[var(--color-muted-foreground)]">{chat.language_code.toUpperCase()}</span>{/if}
 											<span class="text-xs text-[var(--color-muted-foreground)] font-mono">{chat.chat_id}</span>
 										</div>
 										<div class="flex items-center gap-1">