fix: stale update banner after upgrade + skill sync dirty worktree crash

Update checker: only cache registry latest version, always check installed
version fresh — fixes false "0.0.3 → 0.0.4" banner after upgrading.

Skill sync: use git status --porcelain for dirty detection (catches untracked
files), stash with --include-untracked, abort stale rebase on pull failure,
and print tip directing users to skills-local/ for persistent customizations.

Bump @mosaic/mosaic and @mosaic/cli to 0.0.5.

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

packages/mosaic/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@mosaic/mosaic",
-  "version": "0.0.4",
+  "version": "0.0.5",
   "description": "Mosaic agent framework — installation wizard and meta package",
   "type": "module",
   "main": "dist/index.js",