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/commands.ts

@@ -0,0 +1,35 @@
+import type { CommandDefinition } from "../claude-code-command-loader"
+import type { BuiltinCommandName, BuiltinCommands } from "./types"
+import { INIT_DEEP_TEMPLATE } from "./templates/init-deep"
+
+const BUILTIN_COMMAND_DEFINITIONS: Record<BuiltinCommandName, Omit<CommandDefinition, "name">> = {
+  "init-deep": {
+    description: "(builtin) Initialize hierarchical AGENTS.md knowledge base",
+    template: `<command-instruction>
+${INIT_DEEP_TEMPLATE}
+</command-instruction>
+
+<user-request>
+$ARGUMENTS
+</user-request>`,
+    argumentHint: "[--create-new] [--max-depth=N]",
+  },
+}
+
+export function loadBuiltinCommands(
+  disabledCommands?: BuiltinCommandName[]
+): BuiltinCommands {
+  const disabled = new Set(disabledCommands ?? [])
+  const commands: BuiltinCommands = {}
+
+  for (const [name, definition] of Object.entries(BUILTIN_COMMAND_DEFINITIONS)) {
+    if (!disabled.has(name as BuiltinCommandName)) {
+      commands[name] = {
+        name,
+        ...definition,
+      }
+    }
+  }
+
+  return commands
+}