refactor(v2): drop @chat-adapter/shared dep — duck-type NetworkError

The only use was channel-registry.ts checking `err instanceof NetworkError`
to retry transient setup failures. Switched to a duck-type predicate
(`err.name === 'NetworkError'`) so the dep is no longer needed at trunk
level. Channel skills bring it in transitively when they install their
Chat SDK adapter package.

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

package.json

@@ -22,7 +22,6 @@
     "test:watch": "vitest"
   },
   "dependencies": {
-    "@chat-adapter/shared": "^4.24.0",
     "@onecli-sh/sdk": "^0.3.1",
     "better-sqlite3": "11.10.0",
     "chat": "^4.24.0",