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/handler.py

@@ -41,6 +41,36 @@ _rate_limits: TTLCache = TTLCache(maxsize=10000, ttl=3600)
 # Maximum responses per command to avoid Telegram rate limits
 _MAX_RESPONSES_PER_COMMAND = 5
 
+# Commands that fetch assets from the service provider and usually reply
+# with media — "uploading photo" is the accurate UX hint while we wait on
+# the provider API + Telegram upload.
+_UPLOAD_PHOTO_COMMANDS = frozenset({
+    "latest", "random", "favorites", "memory",
+    "search", "find", "person", "place",
+})
+
+# Commands that fetch from the provider but reply with text only.
+# "typing" is accurate; we still want an indicator because the fetch is slow.
+_TYPING_COMMANDS = frozenset({"summary"})
+
+
+def classify_command_chat_action(text: str) -> str | None:
+    """Return the Telegram chat-action hint to show for this command, or None.
+
+    The classification is by command name alone — good enough for the
+    cases where a chat action is worthwhile (slow provider fetches). Fast
+    DB-only commands (``/status``, ``/albums``, ``/events``, ``/people``)
+    return ``None`` and skip the indicator entirely.
+    """
+    cmd, _, _ = parse_command(text)
+    if not cmd:
+        return None
+    if cmd in _UPLOAD_PHOTO_COMMANDS:
+        return "upload_photo"
+    if cmd in _TYPING_COMMANDS:
+        return "typing"
+    return None
+
 
 def _check_rate_limit(bot_id: int, chat_id: str, cmd: str, limits: dict[str, int]) -> int | None:
     """Check rate limit. Returns seconds to wait, or None if OK."""