fix(title): address review nits — gate title-set on persist success, log metadata errors

- Move set_title_if_missing call inside Ok arm so failed message
  persists don't produce ghost titles (ilblackdragon review)
- Log metadata read errors at debug level instead of silently swallowing

[skip-regression-check]

https://claude.ai/code/session_01BsM2KUzdZNBeoLjk7LymZS

Author: claude

src/agent/thread_ops.rs

@@ -1086,7 +1086,9 @@ impl Agent {
             }
         };
 
-        crate::db::set_title_if_missing(store.as_ref(), thread_id, user_input).await;
+        if result.is_some() {
+            crate::db::set_title_if_missing(store.as_ref(), thread_id, user_input).await;
+        }
 
         result
     }

src/db/mod.rs

@@ -514,7 +514,11 @@ pub async fn set_title_if_missing(
             .get("title")
             .and_then(|t| t.as_str())
             .is_some_and(|s| !s.is_empty()),
-        Ok(None) | Err(_) => return,
+        Ok(None) => return,
+        Err(e) => {
+            tracing::debug!("failed to read metadata for title-set: {e}");
+            return;
+        }
     };
 
     if !has_title {