feat(agents): make OmO default agent via build name hack

- Set build agent's display name to 'OmO' (keeps builtIn: true priority)
- Add OmO as subagent (actual execution target when selected)
- Remove explicit tools list from OmO agent (inherit all)
- Rename omo_agent.disable_build to omo_agent.disabled

This hack works around OpenCode's agent selection by key name.
TODO: Use config.default_agent when PR #5313 is released.

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/config/schema.ts

@@ -96,7 +96,7 @@ export const ClaudeCodeConfigSchema = z.object({
 })
 
 export const OmoAgentConfigSchema = z.object({
-  disable_build: z.boolean().optional(),
+  disabled: z.boolean().optional(),
 })
 
 export const OhMyOpenCodeConfigSchema = z.object({