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-tauri/src/ipc.rs

@@ -251,6 +251,8 @@ pub struct PersistedSettings {
     pub is_sidebar_visible: bool,
     pub active_settings_tab: SettingsTab,
     pub scheduler: SchedulerSettings,
+    pub scheduler_running: bool,
+    pub scheduler_active_download_ids: Vec<String>,
     pub scheduler_last_start_key: String,
     pub scheduler_last_stop_key: String,
     pub last_custom_speed_limit_ki_b: u32,