refactor: Remove semantic search and vector embedding functionality

Removes @xenova/transformers dependency, vector storage tables, embedding generation, and semantic search APIs. Simplifies context building to use only FTS search. Eliminates visualizer server, postinstall model download, and related CLI commands. Reduces package size and complexity while maintaining core static analysis capabilities.

__tests__/foundation.test.ts

@@ -275,18 +275,6 @@ describe('CodeGraph Foundation', () => {
       cg.close();
     });
 
-    it('should require embedding initialization for semantic search', async () => {
-      const cg = CodeGraph.initSync(tempDir);
-
-      // Semantic search requires embeddings to be initialized first
-      await expect(cg.semanticSearch('test')).rejects.toThrow(/not initialized/i);
-      await expect(cg.findSimilar('test')).rejects.toThrow(/not initialized/i);
-
-      // Check embedding status
-      expect(cg.isEmbeddingsInitialized()).toBe(false);
-
-      cg.close();
-    });
   });
 });