fix(mosaic): add @mosaic/cli dependency + postinstall hint

@mosaic/mosaic is a metapackage but was missing @mosaic/cli as a dep,
so npm install -g @mosaic/mosaic only gave you mosaic-wizard, not mosaic.

Changes:
- Add @mosaic/cli as dependency (brings in mosaic binary)
- Add postinstall script with guidance message

packages/mosaic/package.json

@@ -20,12 +20,14 @@
     }
   },
   "scripts": {
+    "postinstall": "echo '\nMosaic Stack installed. Run `mosaic-wizard` to bootstrap your config, or `mosaic --help` for CLI commands.\n'",
     "build": "tsc",
     "lint": "eslint src",
     "typecheck": "tsc --noEmit",
     "test": "vitest run --passWithNoTests"
   },
   "dependencies": {
+    "@mosaic/cli": "workspace:*",
     "@mosaic/forge": "workspace:*",
     "@mosaic/macp": "workspace:*",
     "@mosaic/prdy": "workspace:*",