Allow failed runs to always be deleted

Failed runs have no output to protect, so they can be deleted
without checking L2 shared status or activity records.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server.py

@@ -406,6 +406,8 @@ async def discard_run(run_id: str, username: str = Depends(get_required_user)):
     if run.username not in (username, actor_id):
         raise HTTPException(403, "Access denied")
 
+    # Failed runs can always be deleted (no output to protect)
+    if run.status != "failed":
         # Check if activity exists for this run
         activity = cache_manager.get_activity(run_id)