feat(setup): add Linear channel, fix setup permissions

Enable Linear channel adapter. Fix setup permission rules: use specific
npm install entries per adapter package, replace cp -r with rsync -a to
avoid built-in cp safety prompt, add head to allow list for chained
commands. Update Linear API key URL.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -26,7 +26,7 @@
     "@chat-adapter/discord": "^4.24.0",
     "@chat-adapter/gchat": "^4.24.0",
     "@chat-adapter/github": "^4.24.0",
-    "@chat-adapter/linear": "^4.24.0",
+    "@chat-adapter/linear": "^4.26.0",
     "@chat-adapter/slack": "^4.24.0",
     "@chat-adapter/state-memory": "^4.24.0",
     "@chat-adapter/teams": "^4.24.0",