migrate mosaic home to xdg config path

bin/mosaic-migrate-local-skills

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-MOSAIC_HOME="${MOSAIC_HOME:-$HOME/.mosaic}"
+MOSAIC_HOME="${MOSAIC_HOME:-$HOME/.config/mosaic}"
 APPLY=0
 
 usage() {
@@ -9,7 +9,7 @@ usage() {
 Usage: $(basename "$0") [--apply]
 
 Migrate runtime-local skill directories (e.g. ~/.claude/skills/jarvis) to Mosaic-managed
-skills by replacing local directories with symlinks to ~/.mosaic/skills-local.
+skills by replacing local directories with symlinks to ~/.config/mosaic/skills-local.
 
 Default mode is dry-run.
 USAGE