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.

server/__tests__/tmux.test.js

@@ -41,6 +41,16 @@ describe("tmux wrapper", () => {
     );
   });
 
+  it("newSession with no argv leaves tmux its default shell (no trailing --)", () => {
+    const calls = [];
+    tmux.__setExecImpl((args) => {
+      calls.push(args);
+      return "";
+    });
+    tmux.newSession({ name: "agenthub-lane-1", cwd: "C:\\repo", argv: [] });
+    assert.deepEqual(calls[0], ["new-session", "-d", "-s", "agenthub-lane-1", "-c", "C:\\repo"]);
+  });
+
   it("newSession builds the correct argv", () => {
     const calls = [];
     tmux.__setExecImpl((args) => {