fix(messages): use HTML strong tag instead of markdown, remove reply_to mapping from migration

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/migrate_messages.py

@@ -27,7 +27,7 @@ from database import (SessionLocal, PrivateMessage, MessageGroup, MessageGroupMe
 def build_content(subject, content):
     """Prepend subject as bold line if present."""
     if subject and subject.strip():
-        return f"**{subject.strip()}**\n\n{content}"
+        return f"<p><strong>{subject.strip()}</strong></p>{content}"
     return content
 
 
@@ -95,16 +95,15 @@ def migrate_private_messages(db, dry_run):
         for pm in pair_msgs:
             full_content = build_content(pm.subject, pm.content)
 
-            # Resolve reply_to_id from old parent_id
-            reply_to_id = None
-            if pm.parent_id and pm.parent_id in pm_id_map:
-                reply_to_id = pm_id_map[pm.parent_id]
+            # Note: old parent_id was thread-root (email-style), not a specific quote.
+            # Don't map to reply_to_id — it would create visual clutter with every
+            # reply quoting the same root message.
 
             conv_msg = ConvMessage(
                 conversation_id=conv.id,
                 sender_id=pm.sender_id,
                 content=full_content,
-                reply_to_id=reply_to_id,
+                reply_to_id=None,
                 created_at=pm.created_at,
             )
             db.add(conv_msg)