feat(orchestrator): file-based orchestrator request watcher (§14.3)

- domain: OrchestratorRequest/Command parse-don't-validate + OrchestratorRequestProcessed event
- application: OrchestratorService dispatching spawn/stop/update_agent_context
- infrastructure: request watcher over .ideai/requests/, writes .response.json
- app-tauri: relay OrchestratorRequestProcessed to the frontend DTO

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/domain/src/events.rs

@@ -69,6 +69,18 @@ pub enum DomainEvent {
         /// The project.
         project_id: ProjectId,
     },
+    /// An orchestrator request (dropped under `.ideai/requests/`) was processed
+    /// by IdeA on behalf of a requester agent (ARCHITECTURE §14.3). Relayed so the
+    /// frontend can surface orchestration activity; the resulting cell/tab opens
+    /// off the [`AgentLaunched`](Self::AgentLaunched) event for `spawn_agent`.
+    OrchestratorRequestProcessed {
+        /// Id of the requesting (orchestrator) agent — the request subdirectory.
+        requester_id: String,
+        /// The action that was processed (`spawn_agent`, `stop_agent`, …).
+        action: String,
+        /// Whether IdeA handled it successfully.
+        ok: bool,
+    },
     /// Raw PTY output (usually routed to a dedicated channel, not this bus).
     PtyOutput {
         /// The session.