fix: stop tracking sessions that never become ready

When session readiness times out, immediately close the spawned pane and skip tracking to prevent stale mappings from causing reopen and close anomalies.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/tmux-subagent/session-created-handler.ts

@@ -135,10 +135,21 @@ export async function handleSessionCreated(
 
     const sessionReady = await deps.waitForSessionReady(sessionId)
     if (!sessionReady) {
-      log("[tmux-session-manager] session not ready after timeout, tracking anyway", {
+      log("[tmux-session-manager] session not ready after timeout, closing spawned pane", {
         sessionId,
         paneId: result.spawnedPaneId,
       })
+
+      await executeActions(
+        [{ type: "close", paneId: result.spawnedPaneId, sessionId }],
+        {
+          config: deps.tmuxConfig,
+          serverUrl: deps.serverUrl,
+          windowState: state,
+        },
+      )
+
+      return
     }
 
     const now = Date.now()