fix(appview): empty profile instead of 404 for unindexed handles

resolve_profile returned 404 when the requested handle had no
posts in the local index — true for every local-PDS account
that hasn't yet had its posts ingested through the Jetstream
consumer. The UI then surfaced this as a raw 'err: appview:
profile returned 404' toast instead of an empty profile.

Return a profile row with the requested handle and zero counts
instead. The DID is left empty; the UI's 'copy did' button just
copies an empty string and the header falls back to the handle,
which is the right behaviour for a never-indexed local user.

crates/appview/src/routes.rs

@@ -355,13 +355,24 @@ async fn resolve_profile(
     };
 
     let Some(target_did) = target_did else {
-        return Err((
+        // No posts indexed for this handle yet — typical for
-            StatusCode::NOT_FOUND,
+        // local-PDS users whose posts haven't been ingested into
-            Json(json!({
+        // the Jetstream yet (and the AppView indexes only ingested
-                "error": "NotFound",
+        // posts, never queries upstream PDSs for handle→DID
-                "message": "no DID or handle provided, or no posts for that handle",
+        // resolution). Instead of bubbling a 404 to the UI which
-            })),
+        // then shows an error toast instead of an empty profile,
-        ));
+        // synthesise a profile row with the requested handle and
+        // zero counts. The `did` is left empty; the UI's
+        // `displayHandle()` falls back to the handle and the
+        // "copy did" button just copies an empty string.
+        let display = handle_clean.unwrap_or_default();
+        return Ok(Json(ProfileResponse {
+            did: String::new(),
+            handle: display,
+            posts: Vec::new(),
+            followers: 0,
+            following: 0,
+        }));
     };
 
     // Fetch the user's most recent posts (newest first). We return up to