feat: Auto-rename DM rooms by default with improved title prompt

- DM rooms (1:1 with bot) now auto-rename after first response
  without needing !ai auto-rename on
- Group rooms still require explicit opt-in
- Skip rename if room already has a meaningful name
- Improved prompt: emoji prefix, 3-5 words, same language as chat
  (inspired by Open WebUI title generation)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bot.py

@@ -484,8 +484,13 @@ class Bot:
             reply = resp.choices[0].message.content
             await self._send_text(room.room_id, reply)
             # Auto-rename room after first AI response
-            if (room.room_id in self.auto_rename_rooms
-                    and room.room_id not in self.renamed_rooms):
+            # In DMs: always auto-rename. In groups: only if explicitly enabled.
+            is_dm = room.member_count == 2
+            should_rename = (
+                room.room_id not in self.renamed_rooms
+                and (is_dm or room.room_id in self.auto_rename_rooms)
+            )
+            if should_rename:
                 await self._auto_rename_room(room, user_message, reply)
         except Exception:
             logger.exception("LLM call failed")
@@ -529,24 +534,31 @@ class Bot:
         return user_message
 
     async def _auto_rename_room(self, room, user_message: str, ai_reply: str):
-        """Generate a short topic title and set it as the room name."""
+        """Generate a short topic title and set it as the room name (Open WebUI style)."""
+        # Skip if room already has a meaningful name (not default)
+        current_name = getattr(room, "name", "") or ""
+        if current_name and current_name.lower() not in ("", "ai", "empty room", "new chat"):
+            self.renamed_rooms.add(room.room_id)
+            return
+
         try:
             resp = await self.llm.chat.completions.create(
                 model=self.room_models.get(room.room_id, DEFAULT_MODEL),
                 messages=[
-                    {"role": "system", "content": (
-                        "Generate a very short room title (3-6 words, no quotes) "
-                        "that captures the topic of this conversation. "
-                        "Reply with ONLY the title, nothing else."
-                    )},
                     {"role": "user", "content": user_message},
-                    {"role": "assistant", "content": ai_reply[:200]},
-                    {"role": "user", "content": "What is a good short title for this conversation?"},
+                    {"role": "assistant", "content": ai_reply[:300]},
+                    {"role": "user", "content": (
+                        "Generate a concise, 3-5 word title with an emoji as prefix "
+                        "that summarizes the conversation above. "
+                        "Use the same language as the conversation. "
+                        "Do not use quotation marks or formatting. "
+                        "Respond with ONLY the title, nothing else."
+                    )},
                 ],
                 max_tokens=30,
             )
             title = resp.choices[0].message.content.strip().strip('"\'')
-            if not title or len(title) > 80:
+            if not title or len(title) > 80 or len(title) < 3:
                 return
             await self.client.room_put_state(
                 room.room_id, "m.room.name",