feat(semantic-index): remove searchMaxResults user setting, always use default

The "单次检索片段数" input was surfaced in settings but adds noise without
meaningful benefit for most users. Remove the UI control entirely and fix
normalizeConfig to always return SEARCH_MAX_RESULTS_DEFAULT (10), ignoring
any previously saved value so existing custom settings are silently reset to
default on next load.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/node-runtime/src/semantic-index/config.ts

@@ -131,7 +131,7 @@ function normalizeConfig(raw: Partial<SemanticIndexConfig> | null | undefined):
     mode,
     local: { modelId: raw.local?.modelId ?? base.local.modelId },
     api,
-    searchMaxResults: clampSearchMaxResults(raw.searchMaxResults),
+    searchMaxResults: SEARCH_MAX_RESULTS_DEFAULT,
   }
 }