feat(agents): add OmO and OmO-Plan as primary agents, demote build/plan

- OmO: Primary orchestrator (Claude Opus 4.5)
- OmO-Plan: Inherits ALL settings from OpenCode's plan agent at runtime
  - description appended with '(OhMyOpenCode version)'
  - Configurable via oh-my-opencode.json agents.OmO-Plan
- build/plan: Demoted to subagent when OmO enabled
- Add plan and OmO-Plan to OverridableAgentNameSchema

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

src/config/schema.ts

@@ -28,7 +28,9 @@ export const BuiltinAgentNameSchema = z.enum([
 
 export const OverridableAgentNameSchema = z.enum([
   "build",
+  "plan",
   "OmO",
+  "OmO-Plan",
   "oracle",
   "librarian",
   "explore",
@@ -78,7 +80,9 @@ export const AgentOverrideConfigSchema = z.object({
 
 export const AgentOverridesSchema = z.object({
   build: AgentOverrideConfigSchema.optional(),
+  plan: AgentOverrideConfigSchema.optional(),
   OmO: AgentOverrideConfigSchema.optional(),
+  "OmO-Plan": AgentOverrideConfigSchema.optional(),
   oracle: AgentOverrideConfigSchema.optional(),
   librarian: AgentOverrideConfigSchema.optional(),
   explore: AgentOverrideConfigSchema.optional(),