feat(KB-503): add multi-project CLI support with project subcommands

- Add project subcommands: list, add, remove, show, set-default, detect
- Add --project flag support for all task commands
- Create project-context.ts utilities for project resolution
- Add defaultProjectId to GlobalSettings type
- Implement project auto-detection from cwd
- Update CLI argument parsing for global --project flag
- Add multi-project CLI documentation to AGENTS.md

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(KB-050):");
+    expect(String(commitCall![0])).toContain("feat(FN-050):");
   });
 
   it("fallback commit omits task ID when includeTaskIdInCommit is false", async () => {