Refactor subagent and workflow domain models; migrate access tiers and events to domain module

- Moved `AccessTier` and `SubagentEvent` enums to `zesdex_domain::subagent`.
- Consolidated workflow-related types into `zesdex_domain::workflow`.
- Updated references across the codebase to use the new domain models.
- Refactored tool execution logic to utilize a new `ToolExecutor` trait.
- Enhanced `AgentTurnService` to handle tool calls and events more effectively.
- Adjusted API handlers and state management to align with new domain structure.

apps/interfaces/api/src/state.rs

@@ -194,7 +194,7 @@ pub struct ApiState {
     pub token_service: JwtTokenService,
 
     /// LLM provider client for chat completions.
-    pub llm_client: zesdex_infrastructure::llm::LlmClient,
+    pub llm_client: zesdex_infrastructure::llm::provider::LlmClient,
 }
 
 impl fmt::Debug for ApiState {
@@ -272,7 +272,7 @@ impl ApiState {
             zesdex_application::cms::MemoryServiceImpl::new(memory_repo, memory_dir);
 
         let token_service = JwtTokenService::new(&jwt_secret);
-        let llm_client = zesdex_infrastructure::llm::LlmClient::new(
+        let llm_client = zesdex_infrastructure::llm::provider::LlmClient::new(
             llm_api_key.into(),
             llm_model.into(),
             llm_base_url,