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/application/src/orchestrator/mod.rs

@@ -0,0 +1,9 @@
+//! Orchestrator application service (ARCHITECTURE §14.3).
+//!
+//! Turns a validated [`domain::OrchestratorCommand`] into the *same* agent/terminal
+//! use-case calls the UI makes, so an orchestrator agent can drive IdeA without
+//! ever spawning a process itself. See [`service::OrchestratorService`].
+
+mod service;
+
+pub use service::{OrchestratorOutcome, OrchestratorService};