fix(editor): Ctrl/⌘-hover info replaces hover popups instead of stacking (#60)

Root cause: the quick-doc/problem hover and the Ctrl/⌘-hover navigation info were independent tooltips with no precedence, and the navigation modifier was only seen through the focused editor's key events, so holding Ctrl stacked both popups.

Fix: a window-wide platform navigation modifier (`src/platform/navigationModifier.ts`, ⌘ on macOS / Ctrl elsewhere, unchorded); with it held the plain hover doesn't open, late LSP results are dropped, an open hover closes (unless the pointer is inside it, so Ctrl/⌘+C still copies), release clears the link and info.

Siblings: problem/diagnostic hover, debugger value tooltip, inlay hint hovers (no doc or underline through hints, platform-correct Ctrl/⌘-click), consistent ⌘ vs ⌃ handling on macOS.

Verified in the app on macOS (⌘): hover then ⌘ leaves only the nav info, ⌘ before hover shows only nav info, release clears both and plain hover returns. Not verified on Windows.

Fixes #57

https://claude.ai/code/session_01VUYsdXA2nkF5v6zsC93dpn

src/platform/navigationModifier.ts

@@ -0,0 +1,77 @@
+/**
+ * The navigation modifier (⌘ on macOS, Ctrl elsewhere) as a live, window-wide
+ * state: ⌘/Ctrl-hover shows the navigation link and its brief info, and every
+ * plain hover popup (quick documentation, problems, debugger values) yields to
+ * it. Tracked on the window so an editor sees the key even when it isn't focused.
+ */
+import { hasPrimaryModifier, isMacHost } from "./keymap";
+
+type ModifierEvent = Pick<MouseEvent, "metaKey" | "ctrlKey" | "altKey" | "shiftKey">;
+
+/** ⌘/Ctrl alone: no ⌥/⇧ (other gestures) and not the other platform's Ctrl/⌘. */
+export function isNavigationGesture(e: ModifierEvent): boolean {
+  return hasPrimaryModifier(e) && !e.altKey && !e.shiftKey && !(isMacHost() ? e.ctrlKey : e.metaKey);
+}
+
+let held = false;
+let pointer: Element | null = null;
+const listeners = new Set<(held: boolean) => void>();
+let installed: (() => void) | null = null;
+
+function setHeld(value: boolean) {
+  if (held === value) return;
+  held = value;
+  for (const fn of [...listeners]) fn(value);
+}
+
+function install() {
+  if (installed || typeof window === "undefined") return;
+  const onKey = (e: KeyboardEvent) => setHeld(isNavigationGesture(e));
+  // Also from pointer events: a key released outside the window never reports its keyup.
+  const onMouse = (e: MouseEvent) => {
+    pointer = e.target instanceof Element ? e.target : null;
+    setHeld(isNavigationGesture(e));
+  };
+  const onBlur = () => setHeld(false);
+  const opts = { capture: true, passive: true } as const;
+  window.addEventListener("keydown", onKey, opts);
+  window.addEventListener("keyup", onKey, opts);
+  window.addEventListener("mousemove", onMouse, opts);
+  window.addEventListener("mousedown", onMouse, opts);
+  window.addEventListener("blur", onBlur);
+  installed = () => {
+    window.removeEventListener("keydown", onKey, opts);
+    window.removeEventListener("keyup", onKey, opts);
+    window.removeEventListener("mousemove", onMouse, opts);
+    window.removeEventListener("mousedown", onMouse, opts);
+    window.removeEventListener("blur", onBlur);
+    installed = null;
+  };
+}
+
+/** Whether ⌘ (macOS) / Ctrl is held on its own right now. */
+export function navigationModifierHeld(): boolean {
+  install();
+  return held;
+}
+
+/** Element under the pointer at the last mouse move (null before any). */
+export function pointerTarget(): Element | null {
+  install();
+  return pointer;
+}
+
+/** Called with the new state whenever the navigation modifier is pressed or released. */
+export function onNavigationModifier(fn: (held: boolean) => void): () => void {
+  install();
+  listeners.add(fn);
+  return () => listeners.delete(fn);
+}
+
+/** Tests: forget the tracked state and listeners. */
+export function resetNavigationModifier() {
+  installed?.();
+  held = false;
+  pointer = null;
+  listeners.clear();
+}