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/infrastructure/src/lib.rs

@@ -17,6 +17,7 @@ pub mod eventbus;
 pub mod fs;
 pub mod git;
 pub mod id;
+pub mod orchestrator;
 pub mod process;
 pub mod pty;
 pub mod remote;
@@ -28,6 +29,10 @@ pub use eventbus::TokioBroadcastEventBus;
 pub use fs::LocalFileSystem;
 pub use git::Git2Repository;
 pub use id::UuidGenerator;
+pub use orchestrator::{
+    process_request_file, FsOrchestratorWatcher, OrchestratorResponse, OrchestratorWatchHandle,
+    REQUESTS_SUBDIR,
+};
 pub use process::LocalProcessSpawner;
 pub use pty::PortablePtyAdapter;
 pub use remote::{remote_host, LocalHost};