docs(p10-1a-2): note backfill invariant at search_with_opts non-trace path (Task 8 review)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-app/src/app.rs

@@ -426,6 +426,9 @@ impl App {
             });
         }
 
+        // backfill_code_lang + backfill_repo are applied inside `search`
+        // via `search_uncached` — no explicit call needed here. Trace
+        // branch above calls them directly because it bypasses `search`.
         let mut all_hits = self.search(fetch_query)?;
 
         // Skip offset.