fix(agent): support /goal across remote Cursor windows

[chenzetong]

Summary

• register CreateGoal and UpdateGoal across the tool registry, dynamic namespace, protocol serialization, status normalization, and local results
• expose the owning Cursor++ version through /health and let newer extension windows take over older compatible server owners
• reject takeover requests from browser origins or non-loopback clients
• bump the extension to 0.0.16

Root cause

On Remote SSH, another Cursor window could continue owning the global embedded BYOK server with the pre-patch bundle. Reloading only the SSH window left the stale owner alive, so dynamic tool discovery still omitted the Goal tools even after installing a rebuilt extension.

Verification

• TypeScript typecheck
• ESLint
• Vitest: 40 files, 377 tests passed
• production esbuild bundle
• staged diff secret scan: no credentials or sensitive values found

Upgrade note

The already-running 0.0.15 server does not expose a version or takeover endpoint. The first upgrade therefore still requires closing all Cursor windows once before reopening the Remote SSH project. Future version mismatches can hand off automatically.