feat(matrixbot): remove the auto-invite welcome flow entirely

Joining the Lotus Guild Space (join_rule: public) triggered a welcome DM;
reacting to it made the bot invite that user into a fixed room list. Now
that #general is published to the public room directory, any stranger can
join the Space and trigger this.

The room list excluded the invite-only rooms, but it included Voice, whose
join rule is `knock`. An invite bypasses a knock gate, so a stranger could
skip the approval step that rule exists to enforce.

Removes welcome.py, the Space-join watcher in Callbacks.member, both
welcome-reaction hooks, and the admin `cleanwelcome` command. The bot no
longer issues invites automatically anywhere. The PL50+ `invite` and
`inviteall` commands are untouched: those are deliberate admin actions.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

matrixbot/callbacks.py

@@ -14,8 +14,6 @@ from commands import (
     record_nhie_reaction,
     record_hottake_reaction,
 )
-from welcome import handle_welcome_reaction, handle_space_join, SPACE_ROOM_ID
-
 logger = logging.getLogger("matrixbot")
 
 
@@ -95,7 +93,6 @@ class Callbacks:
         key = event.key
         logger.info("reaction: key=%r target=%s sender=%s", key, reacted_event_id[:16], event.sender)
 
-        await handle_welcome_reaction(self.client, room.room_id, event.sender, reacted_event_id, key)
         record_wyr_vote(reacted_event_id, event.sender, key)
         record_acronym_vote(reacted_event_id, event.sender, key)
         record_nhie_reaction(reacted_event_id, event.sender, key)
@@ -119,33 +116,18 @@ class Callbacks:
         key = relates_to.get("key", "")
         logger.info("unknown_event reaction: key=%r target=%s sender=%s", key, reacted_event_id[:16], event.sender)
 
-        await handle_welcome_reaction(self.client, room.room_id, event.sender, reacted_event_id, key)
         record_wyr_vote(reacted_event_id, event.sender, key)
         record_acronym_vote(reacted_event_id, event.sender, key)
         record_nhie_reaction(reacted_event_id, event.sender, key)
         record_hottake_reaction(reacted_event_id, event.sender, key)
 
     async def member(self, room, event):
-        """Handle m.room.member events — watch for Space joins."""
-        # Ignore events from before startup
-        if self.startup_sync_token is None:
-            return
+        """Handle m.room.member events.
 
-        # Only care about the Space
-        if room.room_id != SPACE_ROOM_ID:
-            return
-
-        # Ignore our own membership changes
-        if event.state_key == MATRIX_USER_ID:
-            return
-
-        # Only trigger on joins (not leaves, bans, etc.)
-        if event.membership != "join":
-            return
-
-        # Check if this is a new join (prev was not "join")
-        prev = event.prev_membership if hasattr(event, "prev_membership") else None
-        if prev == "join":
-            return  # Already was a member, this is a profile update or similar
-
-        await handle_space_join(self.client, event.state_key)
+        The Space-join welcome flow was removed deliberately: it DM'd anyone
+        who joined the (public) Space and, on a reaction, invited them into
+        rooms including Voice, whose join rule is `knock`. An invite bypasses
+        that gate, so a stranger could skip the approval step entirely. The
+        bot no longer issues invites of any kind.
+        """
+        return