fix(app): polish workspace navigation surfaces

Use mobile action sheets and long-press file menus while preserving provider context across sheet portals. Keep sidebar and file-pane glyphs on shared visual rails, avoid scrollbar layout shifts, and hide keyboard affordances where shortcuts are unavailable.

packages/app/src/keyboard/availability.test.ts

@@ -0,0 +1,11 @@
+import { describe, expect, it } from "vitest";
+import { keyboardShortcutsAvailable } from "./availability";
+
+describe("keyboardShortcutsAvailable", () => {
+  it("matches the environments where the shortcut dispatcher runs", () => {
+    expect(keyboardShortcutsAvailable({ isNative: false, isCompact: false })).toBe(true);
+    expect(keyboardShortcutsAvailable({ isNative: false, isCompact: true })).toBe(false);
+    expect(keyboardShortcutsAvailable({ isNative: true, isCompact: false })).toBe(false);
+    expect(keyboardShortcutsAvailable({ isNative: true, isCompact: true })).toBe(false);
+  });
+});

packages/app/src/keyboard/availability.ts

@@ -0,0 +1,19 @@
+import { useIsCompactFormFactor } from "@/constants/layout";
+import { isNative } from "@/constants/platform";
+
+interface KeyboardShortcutEnvironment {
+  isNative: boolean;
+  isCompact: boolean;
+}
+
+export function keyboardShortcutsAvailable({
+  isNative: native,
+  isCompact,
+}: KeyboardShortcutEnvironment): boolean {
+  return !native && !isCompact;
+}
+
+export function useKeyboardShortcutsAvailable(): boolean {
+  const isCompact = useIsCompactFormFactor();
+  return keyboardShortcutsAvailable({ isNative, isCompact });
+}