feat: add proxy settings to Settings dialog (Desktop only) (#537)

* feat: add proxy settings to Settings dialog (Desktop only)

Fixes #535 - Desktop app now respects HTTP/HTTPS proxy configuration.

- Add proxy-manager.ts to handle proxy config storage (JSON file in userData)
- Load proxy settings on app startup before Next.js server starts
- Add IPC handlers for get-proxy and set-proxy
- Add proxy settings UI in Settings dialog (Electron only)
- Add translations for en/zh/ja

* fix: improve proxy settings reliability and simplify UI

- Fix server restart race condition (wait for process exit before starting new server)
- Add URL validation (must include http:// or https:// prefix)
- Enable Node.js built-in proxy support (NODE_USE_ENV_PROXY=1)
- Remove "Proxy Exceptions" field (unnecessary for this app)
- Add debug logging for proxy env vars

* refactor: remove duplicate ProxyConfig interface, import from electron.d.ts

electron/main/ipc-handlers.ts

@@ -11,6 +11,12 @@ import {
     updatePreset,
 } from "./config-manager"
 import { restartNextServer } from "./next-server"
+import {
+    applyProxyToEnv,
+    getProxyConfig,
+    type ProxyConfig,
+    saveProxyConfig,
+} from "./proxy-manager"
 
 /**
  * Allowed configuration keys for presets
@@ -209,4 +215,40 @@ export function registerIpcHandlers(): void {
             return setCurrentPreset(id)
         },
     )
+
+    // ==================== Proxy Settings ====================
+
+    ipcMain.handle("get-proxy", () => {
+        return getProxyConfig()
+    })
+
+    ipcMain.handle("set-proxy", async (_event, config: ProxyConfig) => {
+        try {
+            // Save config to file
+            saveProxyConfig(config)
+
+            // Apply to current process environment
+            applyProxyToEnv()
+
+            const isDev = process.env.NODE_ENV === "development"
+
+            if (isDev) {
+                // In development, env vars are already applied
+                // Next.js dev server may need manual restart
+                return { success: true, devMode: true }
+            }
+
+            // Production: restart Next.js server to pick up new env vars
+            await restartNextServer()
+            return { success: true }
+        } catch (error) {
+            return {
+                success: false,
+                error:
+                    error instanceof Error
+                        ? error.message
+                        : "Failed to apply proxy settings",
+            }
+        }
+    })
 }