feat: wire agent.delegate tool with sub-agent configs

- Export createAgentDelegateTool through builtin/index.ts → tools/index.ts
- Register agent.delegate in routing.ts with lazy orchestrator pattern
- Add agent.delegate + agents.list to messaging and coding policy profiles
- Add group:agents tool group to policy.ts
- Add research/code/comms agent config examples to default.yaml
- Add research/code/comms agent configs to user config.yaml
- Add 11 tests for agent-delegate tool (all pass)
- Typecheck clean, no regressions

src/agents/registry.test.ts

@@ -41,6 +41,7 @@ describe('AgentConfigRegistry', () => {
         assistant: {
           system_prompt: 'Be helpful.',
           model_tier: 'default',
+          backend: 'codex',
           tool_profile: 'messaging',
           sandbox: false,
         },
@@ -58,6 +59,7 @@ describe('AgentConfigRegistry', () => {
       }
       expect(assistant.systemPrompt).toBe('Be helpful.');
       expect(assistant.modelTier).toBe('default');
+      expect(assistant.backend).toBe('codex');
       expect(assistant.toolProfile).toBe('messaging');
 
       const coder = registry.get('coder');

src/agents/registry.ts

@@ -5,6 +5,7 @@ export interface AgentConfig {
   name: string;
   systemPrompt?: string;
   modelTier?: ModelTier;
+  backend?: 'native' | 'claude_code' | 'opencode' | 'codex' | 'gemini';
   toolProfile?: ToolProfile;
   toolOverrides?: ToolOverrideConfig;
   sandbox?: boolean;
@@ -39,6 +40,7 @@ export class AgentConfigRegistry {
   loadFromConfig(rawConfigs: Record<string, {
     system_prompt?: string;
     model_tier?: string;
+    backend?: 'native' | 'claude_code' | 'opencode' | 'codex' | 'gemini';
     tool_profile?: string;
     tool_overrides?: ToolOverrideConfig;
     sandbox?: boolean;
@@ -48,6 +50,7 @@ export class AgentConfigRegistry {
         name,
         systemPrompt: raw.system_prompt,
         modelTier: raw.model_tier as ModelTier | undefined,
+        backend: raw.backend,
         toolProfile: raw.tool_profile as ToolProfile | undefined,
         toolOverrides: raw.tool_overrides,
         sandbox: raw.sandbox,