fix(rename): surface duplicate-slug 409 instead of 500 (v1.21.1)

mesh.slug actually carries a UNIQUE constraint (mesh_slug_unique)
even though the schema comment claimed otherwise. Trying to rename
to a slug another mesh already owns blew up as a generic 500.
Now: caught at the route, surfaced as 409 with body
{"error":"slug \"<x>\" is already taken"}; CLI maps it to
EXIT.ALREADY_EXISTS and prints the message.

Schema comment corrected to match DB reality.

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

apps/cli/package.json

@@ -1,6 +1,6 @@
 {
   "name": "claudemesh-cli",
-  "version": "1.21.0",
+  "version": "1.21.1",
   "description": "Peer mesh for Claude Code sessions — CLI + MCP server.",
   "keywords": [
     "claude-code",

apps/cli/src/commands/rename.ts

@@ -63,6 +63,7 @@ export async function rename(oldSlug: string, newSlug: string): Promise<number>
       if (err.status === 401) return EXIT.AUTH_FAILED;
       if (err.status === 403) return EXIT.PERMISSION_DENIED;
       if (err.status === 404) return EXIT.NOT_FOUND;
+      if (err.status === 409) return EXIT.ALREADY_EXISTS;
       if (err.status === 400) return EXIT.INVALID_ARGS;
       return EXIT.INTERNAL_ERROR;
     }