refactor(8.0): remove dead/deprecated code (legacy sweep)

- Deleted getIdsForFilterOld() — a 74-line "DEPRECATED old implementation"
  private method in the metadata index with no callers.
- Deleted getEdgesBySource/ByTarget/ByType from FileSystemStorage — three
  deprecated methods that only `console.warn` + `return []` (stub returns the
  repo forbids); not called anywhere and not required by any interface.
- Removed dead commented-out code fragments (an aspirational find() block in the
  NLP processor; a stale duplicate `const groups` line in the VFS generator).

Build + unit gate green.

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

src/storage/adapters/fileSystemStorage.ts

@@ -661,35 +661,6 @@ export class FileSystemStorage extends BaseStorage {
     return allEdges
   }
 
-  /**
-   * Get edges by source
-   */
-  protected async getEdgesBySource(sourceId: string): Promise<Edge[]> {
-    // This method is deprecated and would require loading metadata for each edge
-    // For now, return empty array since this is not efficiently implementable with new storage pattern
-    console.warn('getEdgesBySource is deprecated and not efficiently supported in new storage pattern')
-    return []
-  }
-
-  /**
-   * Get edges by target
-   */
-  protected async getEdgesByTarget(targetId: string): Promise<Edge[]> {
-    // This method is deprecated and would require loading metadata for each edge
-    // For now, return empty array since this is not efficiently implementable with new storage pattern
-    console.warn('getEdgesByTarget is deprecated and not efficiently supported in new storage pattern')
-    return []
-  }
-
-  /**
-   * Get edges by type
-   */
-  protected async getEdgesByType(type: string): Promise<Edge[]> {
-    // This method is deprecated and would require loading metadata for each edge
-    // For now, return empty array since this is not efficiently implementable with new storage pattern
-    console.warn('getEdgesByType is deprecated and not efficiently supported in new storage pattern')
-    return []
-  }
 
   /**
    * Delete an edge from storage