fix(terminal): psmux wheel scrolling, per-platform tmux upgrade advice, Windows-safe server tests

- Server tests on Windows no longer reach the user's real psmux: psmux
  ignores TMUX_TMPDIR (and 3.3.x PSMUX_DATA_DIR), so quit.test.js's Quit and
  the runner's kill-server ended every live lane pane — the pre-commit hook
  included. scripts/test-server.js now takes tmux off the suites' PATH there.
- Wheel scrolling on Windows: psmux never turns mouse tracking on for its
  client, so xterm.js never reported the wheel and a pane could not scroll.
  A Windows attach is told {type:"wheel"} and the browser sends the SGR wheel
  report itself; psmux scrolls or forwards it to the pane's app.
- tmux.upgradeAdvice(): the oldest tmux AgentHub asks for and how each
  platform upgrades (psmux 3.4.0 -> winget upgrade marlocarlo.psmux; tmux 3.7
  -> brew upgrade tmux / build the release on Linux). Used by the doctor,
  GET /api/run/tmux ({available, version, upgrade}), `agenthub doctor`, and a
  sticky toast on the Workspace page. Advice only: nothing installs tmux.

Committed with --no-verify (user's call): the pre-commit hook runs the full
backend suite, which has ~378 pre-existing failures on Windows (S3/Linux-only
tests: sudo, /proc, systemd, members). Every test touching this change passes:
pty-attach, tmux, run, plugin-doctor-tmux, TerminalView, Workspace, and the
client tests related to the changed files; tsc and the header audit are clean.

server/__tests__/plugin-doctor-tmux.test.js

@@ -3,9 +3,10 @@
  * an install its browser run console cannot work, because every run the
  * dashboard starts is a tmux session (server/lib/tmux.js). The row must WARN
  * and never FAIL: sessions, analytics, lanes and the CLI all work without the
- * binary, so failing a doctor run over it would cry wolf. A tmux older than 3.7
- * (no pane scrollbars) also warns, as does a new binary still talking to an
- * older running server. tmux is faked through the module's own exec seam, so
+ * binary, so failing a doctor run over it would cry wolf. A tmux older than its
+ * platform asks for (tmux.upgradeAdvice: psmux 3.4.0 on Windows, tmux 3.7
+ * elsewhere) also warns, as does a new binary still talking to an older
+ * running server. tmux is faked through the module's own exec seam, so
  * the test never depends on the host having it.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
@@ -56,18 +57,18 @@ describe("plugin-doctor: tmux row", () => {
     assert.equal(rowWithTmux("next-3.8", "3.8-rc3").level, "ok");
   });
 
-  it("warns, with the upgrade path, when tmux is older than 3.7", () => {
-    const row = rowWithTmux("3.4", "3.4");
+  it("warns, with this platform's upgrade path, when tmux is older than it asks for", () => {
+    // 2.9 is too old everywhere; the advice (minimum, command) is per platform.
+    const row = rowWithTmux("2.9", "2.9");
 
     assert.equal(row.level, "warn");
-    assert.match(row.detail, /3\.7/);
-    assert.match(row.detail, /brew upgrade tmux/);
+    assert.ok(row.detail.includes(tmux.upgradeAdvice("2.9")), row.detail);
   });
 
   it("warns when a new tmux is still talking to an older running server", () => {
-    const row = rowWithTmux("3.7c", "3.4");
+    const row = rowWithTmux("3.7c", "2.9");
 
     assert.equal(row.level, "warn");
-    assert.match(row.detail, /server is 3\.4/);
+    assert.match(row.detail, /server is 2\.9/);
   });
 });