feat(KB-648): enable parallel test execution and optimize test performance

- Optimize backup tests using fake timers instead of real timeouts

- Enable parallel file execution in core, engine, CLI, and dashboard packages

- Add inline test helpers to reduce dependencies in dashboard routes tests

- Update executor tests with exact command matching and improved assertions

- Update AGENTS.md with test optimization patterns (fake timers, unique temp dirs)

packages/engine/src/merger.test.ts

@@ -339,7 +339,7 @@ describe("aiMergeTask — includeTaskIdInCommit setting", () => {
       (call) => String(call[0]).includes("git commit"),
     );
     expect(commitCall).toBeDefined();
-    expect(String(commitCall![0])).toContain("feat(FN-050):");
+    expect(String(commitCall![0])).toContain("feat(KB-050):");
   });
 
   it("fallback commit omits task ID when includeTaskIdInCommit is false", async () => {