Add builtin-commands feature with init-deep command and disabled_commands config option

- New src/features/builtin-commands/ module with CommandDefinition loader
- Implements init-deep command for hierarchical AGENTS.md knowledge base generation
- Adds BuiltinCommandName and BuiltinCommandNameSchema to config
- Integrates builtin commands loader into main plugin with proper config merging
- Supports disabling specific builtin commands via disabled_commands config array

🤖 Generated with assistance of https://github.com/code-yeongyu/oh-my-opencode

src/features/builtin-commands/index.ts

@@ -0,0 +1,2 @@
+export * from "./types"
+export * from "./commands"