search: add semantic deduplication to reduce query redundancy

- Implement Jaccard word-level similarity in Search.ts
- Add 15 unit tests for query quality metrics and deduplication
- Introduce optional searchSettings.semanticDedup config flag
- Backward-compatible, default enabled (threshold 0.65)
- Tests: 17/17 pass, typecheck clean, risk: low

src/interface/Config.ts

@@ -54,6 +54,7 @@ export interface ConfigSearchSettings {
     retryMobileSearchAmount: number;
     localFallbackCount?: number; // Number of local fallback queries to sample when trends fail
     extraFallbackRetries?: number; // Additional mini-retry loops with fallback terms
+    semanticDedup?: boolean; // Filter queries with high semantic similarity (default: true)
 }
 
 export interface ConfigSearchDelay {