feat(mosaic): add secure skill registration CLI (#826)

packages/mosaic/framework/defaults/README.md

@@ -181,13 +181,19 @@ The installer rejects unrecognized flags or positional arguments before making c
 
 ## Universal Skills
 
-The installer syncs skills from `mosaic/agent-skills` into `~/.config/mosaic/skills/`, then links each skill into runtime directories.
+The installer syncs skills from `mosaic/agent-skills` into `~/.config/mosaic/skills/`. Install, wizard finalization, and `mosaic update` automatically reconcile every canonical skill into Claude Code's `~/.claude/skills/` directory.
 
 ```bash
-mosaic sync                                    # Full sync (clone + link)
-~/.config/mosaic/bin/mosaic-sync-skills --link-only   # Re-link only
+mosaic sync                         # Full canonical catalog sync
+mosaic skill list                   # Show registered, missing, dangling, and foreign entries
+mosaic skill register <name>        # Register or repair one canonical Claude link
+mosaic skill unregister <name>      # Remove one Mosaic-owned Claude link
 ```
 
+Skill names are direct children using `[A-Za-z0-9][A-Za-z0-9._-]*`, not paths. Registration rejects traversal/control characters and never replaces foreign files, directories, or symlinks; unregister removes only links that point inside the canonical Mosaic skill root. After registering during a running Claude Code session, use `/reload-skills` or start a new session.
+
+M1 lifecycle management targets Claude Code. Pi can discover the canonical Mosaic root through its launcher configuration. Codex parity remains follow-up scope and continues to use the existing full skill-sync linker.
+
 ## Health Audit
 
 ```bash