feat: add telegram notification channel with outbox service and per-user preferences

Extend the notification system with a third channel (telegram) alongside existing in_app and push channels. Add `telegram_enabled` column to `notification_preferences` table, update `NOTIFICATION_CHANNELS` and `_NOTIFICATION_CHANNEL_COLUMNS` mappings, and set telegram default to off (`_NOTIFICATION_CHANNEL_DEFAULTS`). Create `telegram_outbox` table with columns for uid, user_uid, chat_id, text, status, attempts, created_at, and sent_at, plus an index on status/id for efficient polling. Register `TelegramOutboxService` in the service manager lifecycle. Update API documentation strings to describe the new channel and its pairing requirement. Extend admin notification defaults view to include telegram column. Pass `notif_telegram_paired` flag to profile template based on `telegram_store.is_paired()` check. Update `NotificationPrefForm` and `NotificationDefaultForm` model literals to accept "telegram" as a valid channel value.

devplacepy/routers/profile/index.py

@@ -302,6 +302,11 @@ async def profile_page(
         if (tab == "notifications" and can_manage_customization)
         else []
     )
+    notif_telegram_paired = (
+        telegram_store.is_paired(profile_user["uid"])
+        if (tab == "notifications" and can_manage_customization)
+        else False
+    )
 
     base = site_url(request)
     robots = "noindex,follow" if posts_count < 2 else "index,follow"
@@ -363,6 +368,7 @@ async def profile_page(
             "ai_modifier_sync": ai_modifier_sync,
             "ai_modifier_prompt": ai_modifier_prompt,
             "telegram_paired": telegram_paired,
+            "notif_telegram_paired": notif_telegram_paired,
             "can_manage_customization": can_manage_customization,
             "cust_disable_global": customization_prefs["disable_global"],
             "cust_disable_pagetype": customization_prefs["disable_pagetype"],