feat(desktop): Tier B web side — toast actions, Focus Assist gate, folder DnD

- P5-41/35 useTauriToastActions: native rich-toast click → navigate(path) (opens
  the room), quick reply → mx.sendMessage(roomId, m.text). The desktop bridge
  routes message notifications (tag=roomId) to show_rich_toast.
- P5-56 useTauriFocusAssist + focusAssistActiveAtom: a native focus-assist-changed
  event drives the atom, OR'd into the existing quiet-hours gate in
  ClientNonUIFeatures so notifications+sounds suppress during Windows Focus Assist.
- P5-48 recursive folder drag-drop: fileEntries.ts (sync webkitGetAsEntry capture
  → async batched readEntries traversal, path-prefixed names, 500-file cap) wired
  into useFileDrop, reusing the existing upload pipeline. +3 unit tests.

Hooks no-op in the browser. Gates: tsc/eslint/prettier clean, build OK, 559 tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/hooks/useTauriToastActions.ts

@@ -0,0 +1,39 @@
+import { useNavigate } from 'react-router-dom';
+import { MsgType } from 'matrix-js-sdk';
+import { useMatrixClient } from './useMatrixClient';
+import { useTauriEvent } from './useTauri';
+
+/** Payload of the `lotus-notification-activate` event (a plain body click). */
+interface ActivateDetail {
+  path?: string;
+}
+
+/** Payload of the `lotus-notification-reply` event (the inline reply box). */
+interface ReplyDetail {
+  roomId?: string;
+  text?: string;
+}
+
+/**
+ * P5-41 / P5-35 — wire the native WinRT toast's click + quick-reply back into the
+ * client. The Rust side (`show_rich_toast`) dispatches DOM CustomEvents via
+ * `emit_to_web`:
+ *  - `lotus-notification-activate` → route to the room the toast was for, reusing
+ *    the same `useNavigate(path)` mechanism the web `notificationclick` path uses
+ *    (see ClientNonUIFeatures).
+ *  - `lotus-notification-reply` → send the typed reply straight to the room.
+ * No-op outside Tauri (the events never fire).
+ */
+export function useTauriToastActions(): void {
+  const navigate = useNavigate();
+  const mx = useMatrixClient();
+
+  useTauriEvent<ActivateDetail>('lotus-notification-activate', ({ path }) => {
+    if (path) navigate(path);
+  });
+
+  useTauriEvent<ReplyDetail>('lotus-notification-reply', ({ roomId, text }) => {
+    if (!roomId || !text) return;
+    mx.sendMessage(roomId, { msgtype: MsgType.Text, body: text }).catch(() => undefined);
+  });
+}