fix(ui): share one z-order stack across Notes and modals (#3798)

* fix(notes): bring pane above active windows

* fix(notes): align tool window z-order handoff

---------

Co-authored-by: Matyas Fenyves <16389204+uhhgoat@users.noreply.github.com>

static/js/toolWindowZOrder.js

@@ -0,0 +1,29 @@
+export const TOOL_WINDOW_SELECTOR = 'body > .modal, body > .research-overlay, body > .notes-pane-backdrop';
+
+export function topToolWindowZ(options = {}) {
+  const {
+    exclude = null,
+    root = globalThis.document,
+    getStyle = globalThis.getComputedStyle,
+    floor = 250,
+  } = options;
+  let top = floor;
+  if (!root || typeof root.querySelectorAll !== 'function' || typeof getStyle !== 'function') return top;
+  root.querySelectorAll(TOOL_WINDOW_SELECTOR).forEach(el => {
+    if (!el || el === exclude) return;
+    if (el.classList?.contains('hidden') || el.classList?.contains('modal-minimized')) return;
+    const cs = getStyle(el);
+    if (cs.display === 'none' || cs.visibility === 'hidden') return;
+    const z = parseInt(cs.zIndex, 10);
+    if (Number.isFinite(z)) top = Math.max(top, z);
+  });
+  return top;
+}
+
+export function nextToolWindowZ(options = {}) {
+  const { current = null } = options;
+  const top = topToolWindowZ(options);
+  const currentZ = parseInt(current, 10);
+  if (Number.isFinite(currentZ) && currentZ > top) return currentZ;
+  return top + 1;
+}