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/proxy-manager.ts

@@ -0,0 +1,75 @@
+import { app } from "electron"
+import * as fs from "fs"
+import * as path from "path"
+import type { ProxyConfig } from "../electron.d"
+
+export type { ProxyConfig }
+
+const CONFIG_FILE = "proxy-config.json"
+
+function getConfigPath(): string {
+    return path.join(app.getPath("userData"), CONFIG_FILE)
+}
+
+/**
+ * Load proxy configuration from JSON file
+ */
+export function loadProxyConfig(): ProxyConfig {
+    try {
+        const configPath = getConfigPath()
+        if (fs.existsSync(configPath)) {
+            const data = fs.readFileSync(configPath, "utf-8")
+            return JSON.parse(data) as ProxyConfig
+        }
+    } catch (error) {
+        console.error("Failed to load proxy config:", error)
+    }
+    return {}
+}
+
+/**
+ * Save proxy configuration to JSON file
+ */
+export function saveProxyConfig(config: ProxyConfig): void {
+    try {
+        const configPath = getConfigPath()
+        fs.writeFileSync(configPath, JSON.stringify(config, null, 2), "utf-8")
+    } catch (error) {
+        console.error("Failed to save proxy config:", error)
+        throw error
+    }
+}
+
+/**
+ * Apply proxy configuration to process.env
+ * Must be called BEFORE starting the Next.js server
+ */
+export function applyProxyToEnv(): void {
+    const config = loadProxyConfig()
+
+    if (config.httpProxy) {
+        process.env.HTTP_PROXY = config.httpProxy
+        process.env.http_proxy = config.httpProxy
+    } else {
+        delete process.env.HTTP_PROXY
+        delete process.env.http_proxy
+    }
+
+    if (config.httpsProxy) {
+        process.env.HTTPS_PROXY = config.httpsProxy
+        process.env.https_proxy = config.httpsProxy
+    } else {
+        delete process.env.HTTPS_PROXY
+        delete process.env.https_proxy
+    }
+}
+
+/**
+ * Get current proxy configuration (from process.env)
+ */
+export function getProxyConfig(): ProxyConfig {
+    return {
+        httpProxy: process.env.HTTP_PROXY || process.env.http_proxy || "",
+        httpsProxy: process.env.HTTPS_PROXY || process.env.https_proxy || "",
+    }
+}