feat(commands): keep chat-action hint alive during slow command fetches

Slow bot commands (/latest, /random, /favorites, /memory, /search,
/find, /person, /place, /summary) spend most of their wall time
fetching assets from the service provider, not uploading to Telegram.
Telegram chat actions expire after ~5s, so the previous one-shot hint
vanished long before media arrived — users saw nothing happening.

- TelegramClient.start_chat_action_keepalive: promoted from private
  helper to public API, posts the action every 4s until cancelled.
- telegram_send.telegram_chat_action: async context manager that
  starts the keep-alive task on enter and cancels + awaits it on
  exit. A None action makes it a no-op so callers don't branch.
- classify_command_chat_action: maps command name to the right
  Telegram action (upload_photo for media-returning commands, typing
  for /summary, None for fast DB-only commands like /status /events).
- webhook.py + telegram_poller.py: wrap handle_command in the context
  manager so the hint persists through the whole fetch+upload window
  in both webhook and long-poll modes.

packages/server/src/notify_bridge_server/commands/webhook.py

@@ -15,8 +15,9 @@ from notify_bridge_core.notifications.telegram.client import TelegramClient
 from ..database.engine import get_session
 from ..database.models import TelegramBot, TelegramChat
 from ..services.telegram import save_chat_from_webhook
+from ..services.telegram_send import telegram_chat_action
 from .base import CommandResponse
-from .handler import handle_command, send_media_group, send_reply
+from .handler import classify_command_chat_action, handle_command, send_media_group, send_reply
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -95,14 +96,17 @@ async def telegram_webhook(
             return {"ok": True, "skipped": "commands_disabled"}
         effective_lang = chat_row.language_override or msg_language
         message_id = message.get("message_id")
-        responses = await handle_command(bot, chat_id, text, language_code=effective_lang)
-        if responses:
-            for resp in responses:
-                if resp.text:
-                    await send_reply(bot_token, chat_id, resp.text, reply_to_message_id=message_id)
-                if resp.media:
-                    await send_media_group(bot_token, chat_id, resp.media, reply_to_message_id=message_id)
-            return {"ok": True}
+        async with telegram_chat_action(
+            bot_token, chat_id, classify_command_chat_action(text),
+        ):
+            responses = await handle_command(bot, chat_id, text, language_code=effective_lang)
+            if responses:
+                for resp in responses:
+                    if resp.text:
+                        await send_reply(bot_token, chat_id, resp.text, reply_to_message_id=message_id)
+                    if resp.media:
+                        await send_media_group(bot_token, chat_id, resp.media, reply_to_message_id=message_id)
+                return {"ok": True}
 
     return {"ok": True, "skipped": "not_a_command"}