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/terminal/registry.rs

@@ -10,7 +10,7 @@ use std::collections::HashMap;
 use std::sync::Mutex;
 
 use domain::ports::PtyHandle;
-use domain::{SessionId, TerminalSession};
+use domain::{AgentId, SessionId, SessionKind, TerminalSession};
 
 /// A registered, live terminal: its PTY handle plus the domain snapshot.
 #[derive(Debug, Clone)]
@@ -59,6 +59,21 @@ impl TerminalSessions {
             .and_then(|m| m.get(id).map(|e| e.session.clone()))
     }
 
+    /// Returns the [`SessionId`] of the live session hosting a given agent, if any.
+    ///
+    /// An agent runs in a session tagged [`SessionKind::Agent`]; this is the
+    /// mapping the orchestrator's `stop_agent` uses to translate an agent id into
+    /// the [`SessionId`] that `CloseTerminal` expects. Returns `None` when the
+    /// agent has no live session (already stopped / never launched).
+    #[must_use]
+    pub fn session_for_agent(&self, agent_id: &AgentId) -> Option<SessionId> {
+        self.entries.lock().ok().and_then(|m| {
+            m.values()
+                .find(|e| matches!(e.session.kind, SessionKind::Agent { agent_id: a } if &a == agent_id))
+                .map(|e| e.session.id)
+        })
+    }
+
     /// Returns the [`PtyHandle`]s of every currently-registered session.
     ///
     /// Used at application shutdown to kill all live PTYs cleanly (the