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/application/src/lib.rs

@@ -33,6 +33,7 @@
 pub mod auth;
 pub mod cms;
 pub mod ports;
+pub mod agent;
 
 // Re-export port traits for ergonomic access.
 pub use ports::*;
@@ -49,3 +50,5 @@ pub use cms::{
     memory_service::MemoryServiceImpl,
     settings_service::SettingsServiceImpl,
 };
+
+pub use agent::{AgentTurnService, ToolExecutor, turn_service::{AgentTurnServiceImpl, compact_messages_with_ai}};