fix: v2.5.6 — Windows panes without sh, UI build without node on PATH

- Windows panes: a WinGet tmux runs native programs and there is no `sh`, so
  every pane's `sh -c` wrapper died at once ("Command failed: tmux set-option
  … mouse on"). paneArgv runs the CLI itself on win32, and a Terminal gets
  tmux's own default shell (newSession drops the `--` for an empty argv).
- Plugin UI build: client deps install with --ignore-scripts and tsc/vite run
  by the running node instead of `npm run build`. On Windows esbuild's
  postinstall went through cmd.exe with no `node` on the server's PATH, both
  installs failed, and Update now kept the previous UI. A test keeps the two
  build steps equal to client/package.json's build script.
- Update all: Atomics.wait instead of a `sleep` binary Windows lacks.

scripts/cc-update-all-helper.js

@@ -187,7 +187,8 @@ function reloadPanes() {
         // `/reload-plugins /reload-skills` — see SETTLE_MS in
         // server/lib/cc-reload.js. Blocking is fine here: this worker is
         // detached and serves no requests.
-        if (!first) execFileSync("sleep", ["1"], { timeout: 15_000 });
+        // Atomics.wait, not `sleep`: Windows has no sleep binary.
+        if (!first) Atomics.wait(new Int32Array(new SharedArrayBuffer(4)), 0, 0, 1000);
         first = false;
         execFileSync("tmux", ["send-keys", "-t", `=${name}:`, "-l", command], { timeout: 15_000 });
         execFileSync("tmux", ["send-keys", "-t", `=${name}:`, "Enter"], { timeout: 15_000 });