COD-104 fix: skip remote tmux prereq check under VITEST (test-mode)

COD-104 wired checkRemoteTmuxAvailable into the remote-session create path,
but it does a real `ssh` via exec — so 2 remote-create tests in
session-routes.test.ts hit a ~10s ssh timeout and failed (422). Mirror
TmuxManager's IS_TEST_MODE no-op-shell-under-VITEST: short-circuit the live
probe to {ok:true} under vitest. Command construction stays covered by
buildRemoteTmuxCheckCommand unit tests. session-routes.test.ts now 61/61.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
(cherry picked from commit 6ae2c0b8160090a1f0f6b32a3fe8496d402ac2c6)

src/remote-hosts.ts

@@ -173,6 +173,14 @@ export interface RemoteTmuxCheckResult {
 export async function checkRemoteTmuxAvailable(
   host: Pick<RemoteHost, 'username' | 'host' | 'port'> & RemoteSshOptions
 ): Promise<RemoteTmuxCheckResult> {
+  // Under vitest, never open a real ssh connection — mirrors TmuxManager's
+  // no-op-shell-under-VITEST (IS_TEST_MODE). Without this, remote-case
+  // create-path tests hit a real ~10s ssh timeout. The command construction is
+  // covered by buildRemoteTmuxCheckCommand unit tests; only the live probe is
+  // short-circuited here.
+  if (process.env.VITEST) {
+    return { ok: true, tmuxPath: '(test-mode)' };
+  }
   const command = buildRemoteTmuxCheckCommand(host);
   try {
     const { stdout } = await execAsync(command, { timeout: 15_000 });