feat: collapse mesh.name and mesh.slug into one identifier (v1.21.0)

Pre-launch fix: every visible surface already keyed on slug, so
"name" was a parallel string that only existed to confuse users
on rename ("I renamed but nothing visible changed").

Now slug IS the identifier. claudemesh rename <old> <new> is the
whole rename surface. PATCH /api/cli/meshes/:slug body becomes
{ slug } and the route writes both columns to keep them in sync.
Mesh create derives slug from input.name and stores name = slug.
Pickers drop the (parens). The claudemesh slug verb shipped 30
min ago is removed — merged into rename.

The mesh.name DB column stays for now to avoid touching ~25
reader sites; a follow-up migration drops it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/cli/package.json

@@ -1,6 +1,6 @@
 {
   "name": "claudemesh-cli",
-  "version": "1.20.1",
+  "version": "1.21.0",
   "description": "Peer mesh for Claude Code sessions — CLI + MCP server.",
   "keywords": [
     "claude-code",