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/services/telegram_poller.py

@@ -257,7 +257,13 @@ async def _poll_bot(bot_id: int) -> None:
     _last_update_id[bot_id] = updates[-1]["update_id"]
 
     # Process each update
-    from ..commands.handler import handle_command, send_media_group, send_reply
+    from ..commands.handler import (
+        classify_command_chat_action,
+        handle_command,
+        send_media_group,
+        send_reply,
+    )
+    from .telegram_send import telegram_chat_action
 
     for update in updates:
         message = update.get("message")
@@ -295,13 +301,16 @@ async def _poll_bot(bot_id: int) -> None:
                         continue
                     effective_lang = chat_row.language_override or msg_language
                 message_id = message.get("message_id")
-                responses = await handle_command(bot_obj, 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)
+                async with telegram_chat_action(
+                    bot_token, chat_id, classify_command_chat_action(text),
+                ):
+                    responses = await handle_command(bot_obj, 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)
             except Exception:
                 _LOGGER.error("Error handling command from bot %d", bot_id, exc_info=True)