fix: harden scheduler, permissions, and download safety

- Implement scheduler hydration barrier to prevent premature triggers
- Track scheduler exact runs using keys to avoid false stops
- Use 'System Events' for accurate macOS automation permissions
- Prevent system-sleep via proper idle assertions
- Ensure download pauses use channel acknowledgements (PauseWithAck)
- Require Firelink ownership before replacing files in add/conflict UI
- Retain partial download assets when removing entries without deletion
- Clear progress state in store when downloads complete or pause to reduce churn
- Handle empty/invalid queue selections gracefully

src/store/downloadStore.test.ts

@@ -0,0 +1,23 @@
+import { beforeEach, describe, expect, it } from 'vitest';
+import { useDownloadProgressStore } from './downloadStore';
+
+describe('useDownloadProgressStore', () => {
+  beforeEach(() => {
+    useDownloadProgressStore.setState({ progressMap: {} });
+  });
+
+  it('prunes terminal progress entries', () => {
+    useDownloadProgressStore.getState().updateDownloadProgress('download-1', {
+      id: 'download-1',
+      fraction: 0.5,
+      speed: '1 MB/s',
+      eta: '10s',
+      size: '2 MB',
+      size_is_final: false
+    });
+
+    useDownloadProgressStore.getState().clearDownloadProgress('download-1');
+
+    expect(useDownloadProgressStore.getState().progressMap).toEqual({});
+  });
+});