feat(tools): harden scheduler speed limiter logs

Modernize the Tools release surfaces for the cross-platform re-release checklist.

- make Speed Limiter presets unit-aware and persist custom removable quick presets

- keep diagnostic logging opt-in on clean installs and honor the saved log state on startup

- stage Scheduler enablement edits without discarding unsaved draft changes

- extend persisted settings and bindings for log opt-in and speed preset state

Verification:

- npm run build

- npm test -- --run src/store/useDownloadStore.test.ts

- cargo test --lib

- cargo test settings --lib

src-tauri/src/ipc.rs

@@ -249,6 +249,8 @@ pub struct PersistedSettings {
     pub approved_download_roots: Vec<String>,
     pub max_concurrent_downloads: usize,
     pub global_speed_limit: String,
+    pub speed_limit_preset_values: Vec<f64>,
+    pub logs_enabled: bool,
     pub is_sidebar_visible: bool,
     pub active_settings_tab: SettingsTab,
     pub scheduler: SchedulerSettings,