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.

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "agenthub",
-  "version": "2.5.5",
+  "version": "2.5.6",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "agenthub",
-      "version": "2.5.5",
+      "version": "2.5.6",
       "hasInstallScript": true,
       "license": "UNLICENSED",
       "dependencies": {