feat(babysitting): make unstable-agent-babysitter always-on by default

Remove the 'enabled' flag from babysitting config - the hook now runs
automatically when not disabled via disabled_hooks. This simplifies
configuration and makes the unstable model monitoring a default behavior.

BREAKING CHANGE: babysitting.enabled config option is removed. Use
disabled_hooks: ['unstable-agent-babysitter'] to disable the hook instead.

assets/oh-my-opencode.schema.json

@@ -2924,10 +2924,6 @@
     "babysitting": {
       "type": "object",
       "properties": {
-        "enabled": {
-          "default": false,
-          "type": "boolean"
-        },
         "timeout_ms": {
           "default": 120000,
           "type": "number"