chore: bump to 2.0.0 with v2 CHANGELOG entry

Major version for the v2 rewrite. CHANGELOG documents the breaking
changes users will hit on upgrade: new entity model, two-DB session
split, `bash nanoclaw.sh` as default install, channels/providers
relocated to sibling branches, three-level isolation, Apple Container
removed from default setup.

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "nanoclaw",
-  "version": "1.2.52",
+  "version": "2.0.0",
   "description": "Personal Claude assistant. Lightweight, secure, customizable.",
   "type": "module",
   "packageManager": "pnpm@10.33.0",