fix: address multiple bugs found in code review

- Fix dirty-user flush race: discard IDs individually after successful save
- Escape LIKE wildcards in LLM-generated topic keywords for DB queries
- Anonymize absent-member aliases to prevent LLM de-anonymization
- Pass correct MIME type to vision model based on image file extension
- Use enumerate instead of list.index() in bcs-scan loop
- Allow bot @mentions with non-report intent to fall through to moderation

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

cogs/commands.py

@@ -320,9 +320,8 @@ class CommandsCog(commands.Cog):
             f"Scanning {len(messages)} messages... (first request may be slow while model loads)"
         )
 
-        for msg in messages:
+        for idx, msg in enumerate(messages):
             # Build context from the messages before this one
-            idx = messages.index(msg)
             ctx_msgs = messages[max(0, idx - 3):idx]
             context = (
                 " | ".join(f"{m.author.display_name}: {m.content}" for m in ctx_msgs)