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/domain/src/workflow/mod.rs

@@ -0,0 +1,45 @@
+//! Workflow and Hive-mind domain models.
+
+/// A single phase in a parsed workflow script.
+#[derive(Debug, Clone)]
+pub struct WorkflowPhase {
+    pub name: String,
+    pub directive: String,
+}
+
+/// A parsed workflow script with named phases.
+#[derive(Debug, Clone)]
+pub struct WorkflowScript {
+    pub name: String,
+    pub phases: Vec<WorkflowPhase>,
+}
+
+/// A directive for a single processing node in the hive mind.
+#[derive(Debug, Clone)]
+pub struct NodeDirective {
+    pub directive: String,
+    pub access_tier: String,
+}
+
+/// A cognitive cycle plan — ordered list of cycles, each containing
+/// parallel node directives.
+#[derive(Debug, Clone)]
+pub struct CognitiveCyclePlan {
+    pub cycles: Vec<Vec<NodeDirective>>,
+}
+
+/// A single cycle in a cognitive cycle plan — parallel node directives
+/// executed together.
+#[derive(Debug, Clone)]
+pub struct CognitiveCycle {
+    pub index: u32,
+    pub directives: Vec<NodeDirective>,
+}
+
+/// Output from a single hive-mind processing node after a cycle completes.
+#[derive(Debug, Clone)]
+pub struct NodeOutput {
+    pub id: String,
+    pub directive: String,
+    pub output: String,
+}