feat: implement settings engine with directory picker and aria2 configuration sync

src/App.tsx

@@ -34,7 +34,7 @@ function App() {
   const doneCount = downloads.filter(download => download.status === 'completed').length;
   const schedulerRunning = useSettingsStore(state => state.schedulerRunning);
   const globalSpeedLimit = useSettingsStore(state => state.globalSpeedLimit);
-  const previousSpeedLimit = useRef(globalSpeedLimit);
+  const previousSpeedLimit = useRef<string | null>(null);
   const maxConcurrentDownloads = useSettingsStore(state => state.maxConcurrentDownloads);
 
   const startSidebarResize = (event: React.PointerEvent<HTMLDivElement>) => {

src/components/SettingsView.tsx

@@ -5,6 +5,7 @@ import {
   SettingsTab,
   useSettingsStore
 } from '../store/useSettingsStore';
+import { useDirectoryPicker } from '../hooks/useDirectoryPicker';
 import {
   Download, Palette, Globe, Folder, Key,
   Moon, Terminal, Puzzle, Info, Plus, Trash2, Copy, RefreshCw, Code
@@ -29,6 +30,7 @@ const settingsTabs: { type: SettingsTab; label: string; icon: typeof Download }[
 
 export default function SettingsView() {
   const settings = useSettingsStore();
+  const { pickDirectory } = useDirectoryPicker();
   const activeTab = settings.activeSettingsTab;
 
   // Local state for versions
@@ -537,6 +539,30 @@ export default function SettingsView() {
           {/* Locations Pane */}
           {activeTab === 'locations' && (
             <div className="settings-pane max-w-[760px]">
+              <div className="mac-settings-group">
+                <div className="mac-settings-row">
+                  <span className="text-[13px] font-semibold text-text-primary">Default Download Path</span>
+                  <div className="flex gap-2">
+                    <input
+                      type="text"
+                      value={settings.defaultDownloadPath || ''}
+                      onChange={(e) => settings.setDefaultDownloadPath(e.target.value)}
+                      className="app-control w-64 text-[11px] px-2"
+                      placeholder="~/Downloads"
+                    />
+                    <button
+                      onClick={async () => {
+                        const path = await pickDirectory(settings.defaultDownloadPath);
+                        if (path) settings.setDefaultDownloadPath(path);
+                      }}
+                      className="app-button px-3 text-xs text-text-secondary hover:bg-item-hover"
+                    >
+                      Browse
+                    </button>
+                  </div>
+                </div>
+              </div>
+
               <div className="mac-settings-group">
                 <label className="mac-settings-row cursor-default">
                   <span className="text-[13px] text-text-primary">Ask where to save each file</span>

src/hooks/useDirectoryPicker.ts

@@ -0,0 +1,22 @@
+import { open } from '@tauri-apps/plugin-dialog';
+
+export const useDirectoryPicker = () => {
+  const pickDirectory = async (defaultPath?: string): Promise<string | null> => {
+    try {
+      const selected = await open({
+        directory: true,
+        multiple: false,
+        defaultPath: defaultPath,
+      });
+      if (selected && typeof selected === 'string') {
+        return selected;
+      }
+      return null;
+    } catch (e) {
+      console.error('Failed to pick directory:', e);
+      return null;
+    }
+  };
+
+  return { pickDirectory };
+};

src/store/settingsStore.ts

@@ -0,0 +1,66 @@
+import { create } from 'zustand';
+import { persist, createJSONStorage, StateStorage } from 'zustand/middleware';
+import { LazyStore } from '@tauri-apps/plugin-store';
+
+export const tauriStore = new LazyStore('store.bin');
+
+const tauriStorage: StateStorage = {
+  getItem: async (name: string): Promise<string | null> => {
+    if (name === 'firelink-engine-settings') {
+      try {
+        const data = await tauriStore.get<string>('engine_settings');
+        return data || null;
+      } catch (e) {
+        console.error("Failed to load engine settings from DB", e);
+        return null;
+      }
+    }
+    return null;
+  },
+  setItem: async (name: string, value: string): Promise<void> => {
+    if (name === 'firelink-engine-settings') {
+      try {
+        await tauriStore.set('engine_settings', value);
+        await tauriStore.save();
+      } catch (e) {
+        console.error("Failed to save engine settings to DB", e);
+      }
+    }
+  },
+  removeItem: async (_name: string): Promise<void> => {
+    // no-op for now
+  },
+};
+
+export interface SettingsState {
+  defaultDownloadPath: string;
+  globalSpeedLimit: number;
+  concurrentDownloads: number;
+
+  setDefaultDownloadPath: (path: string) => void;
+  setGlobalSpeedLimit: (limit: number) => void;
+  setConcurrentDownloads: (count: number) => void;
+}
+
+export const useSettingsStore = create<SettingsState>()(
+  persist(
+    (set) => ({
+      defaultDownloadPath: '~/Downloads',
+      globalSpeedLimit: 0,
+      concurrentDownloads: 3,
+
+      setDefaultDownloadPath: (path) => set({ defaultDownloadPath: path }),
+      setGlobalSpeedLimit: (limit) => set({ globalSpeedLimit: limit }),
+      setConcurrentDownloads: (count) => set({ concurrentDownloads: count }),
+    }),
+    {
+      name: 'firelink-engine-settings',
+      storage: createJSONStorage(() => tauriStorage),
+      partialize: (state) => ({
+        defaultDownloadPath: state.defaultDownloadPath,
+        globalSpeedLimit: state.globalSpeedLimit,
+        concurrentDownloads: state.concurrentDownloads,
+      }),
+    }
+  )
+);