Fix X bot rejecting mentions without conversation_id

**Problem:**
- X API sometimes doesn't include conversation_id for replies
- Bot was rejecting these mentions and moving them to errors
- This was preventing void from responding to many valid mentions

**Solution:**
- When conversation_id is None, use referenced tweet ID as conversation root
- For replies, extract the replied_to tweet ID and use it for thread context
- If no referenced tweets, treat mention as standalone (use mention ID itself)
- Changed from hard rejection (return None) to graceful fallback

**Result:**
- Bot now handles replies without conversation_id properly
- Thread context can still be retrieved using the referenced tweet
- No valid mentions are rejected due to missing conversation_id

🤖 Generated with Claude Code

Co-Authored-By: Claude <[e-mail]>

x.py

···
             logger.info(f"     Reference {i+1}: {ref.get('type')} -> {ref.get('id')}")
         logger.info(f"   Text preview: {mention_text[:100]}...")
         
+        # If no conversation_id, try to use referenced tweet as conversation root
+        if not conversation_id and referenced_tweets:
+            # For replies, use the tweet being replied to as conversation root
+            for ref in referenced_tweets:
+                if ref.get('type') == 'replied_to':
+                    conversation_id = ref.get('id')
+                    logger.info(f"📎 No conversation_id, using replied_to tweet {conversation_id} as conversation root")
+                    break
+        
         if not conversation_id:
-            logger.warning(f"❌ No conversation_id found for mention {mention_id} - this may cause thread context issues")
-            return None
+            # If still no conversation ID, use the mention itself as a standalone
+            conversation_id = mention_id
+            logger.warning(f"⚠️ No conversation_id found for mention {mention_id} - treating as standalone tweet")
         
         # Get thread context with caching enabled for efficiency
         # Use mention_id as until_id to exclude tweets that occurred after this mention