add ranked search to pql sidebar with DSL toggle

Search tab defaults to ranked text search via pql search — debounced
300ms, scored results with visual score bar.  DSL toggle switches to
raw PQL query mode for SQL-like queries.  Clicking a search result
opens it in the markdown context viewer.

Adds pql.search IPC command and PqlClient.search method.  Controller
gains SearchMode enum and search() method alongside existing runQuery.

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

lib/src/pql/client.dart

@@ -59,6 +59,12 @@ class PqlClient {
     return _runList(args);
   }
 
+  Future<List<Map<String, Object?>>> search(String terms, {int? limit}) async {
+    final args = ['search', terms];
+    if (limit != null) args.addAll(['--limit', '$limit']);
+    return _runList(args);
+  }
+
   Future<Map<String, Object?>> doctor() async {
     return _runObject(['doctor']);
   }