feat: integrate worktree isolation into E2E test infrastructure

Add createTestWorktree(), harvestAndCleanup(), and describeWithWorktree()
helpers to e2e-helpers.ts. Add harvest field to EvalTestEntry for
eval-store integration. Register lib/worktree.ts as a global touchfile.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test/helpers/eval-store.ts

@@ -80,6 +80,13 @@ export interface EvalTestEntry {
   missed_bugs?: string[];
 
   error?: string;
+
+  // Worktree harvest data
+  harvest?: {
+    filesChanged: number;
+    patchPath: string;
+    isDuplicate: boolean;
+  };
 }
 
 export interface EvalResult {