feat(agent): inject TTS [[tts]] directive guidance when auto mode is "tagged"

- Add TTSAutoMode field to LoopConfig, Loop, SystemPromptConfig
- Wire from config.Tts.Auto through resolver to system prompt
- Inject "## Voice Response" section explaining [[tts]] usage
- Update AGENTS.md: voice only when user explicitly requests

cmd/gateway_managed.go

@@ -235,6 +235,7 @@ func wireExtras(
 		SkillTenantCfgs:        stores.SkillTenantCfgs,
 		SystemConfigs:          stores.SystemConfigs,
 		Workspace:              workspace,
+		TTSAutoMode:            appCfg.Tts.Auto,
 		AutoInjector:           autoInjector,
 		EvolutionMetricsStore:  stores.EvolutionMetrics,
 		DomainBus:              domainBus,