fix(macp): wire commander dep, registerMacpCommand export, and CLI registration

Add commander dependency to @mosaicstack/macp, export registerMacpCommand
from the package index, and register the macp command in the mosaic CLI.
These were missing from the previous rebase due to conflicting parallel
task merges. Ref CU-05-08.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/macp/package.json

@@ -21,6 +21,9 @@
     "typecheck": "tsc --noEmit",
     "test": "vitest run --passWithNoTests"
   },
+  "dependencies": {
+    "commander": "^13.0.0"
+  },
   "devDependencies": {
     "@types/node": "^22.0.0",
     "@vitest/coverage-v8": "^2.0.0",