feat(electron): add desktop application support with electron (#344)

* feat(electron): add desktop application support with electron

- implement complete Electron main process architecture with window management,
  app menu, IPC handlers, and settings window
- integrate Next.js server for production builds with embedded standalone server
- add configuration management with persistent storage and env file support
- create preload scripts with secure context bridge for renderer communication
- set up electron-builder configuration for multi-platform packaging (macOS,
  Windows, Linux)
- add GitHub Actions workflow for automated release builds
- include development scripts for hot-reload during Electron development

* feat(electron): enhance security and stability

- encrypt API keys using Electron safeStorage API before persisting to disk
- add error handling and rollback for preset switching failures
- extract inline styles to external CSS file and remove unsafe-inline from CSP
- implement dynamic port allocation with automatic fallback for production builds

* fix(electron): add maintainer field for Linux .deb package

- add maintainer email to linux configuration in electron-builder.yml
- required for building .deb packages

* fix(electron): use shx for cross-platform file copying

- replace Unix-only cp -r with npx shx cp -r
- add shx as devDependency for Windows compatibility

* fix(electron): fix runtime icon path for all platforms

- use icon.png directly instead of platform-specific formats
- electron-builder handles icon conversion during packaging
- macOS uses embedded icon from app bundle, no explicit path needed
- add icon.png to extraResources for Windows/Linux runtime access

* fix(electron): add security warning for plaintext API key storage

- warn user when safeStorage is unavailable (Linux without keyring)
- fail secure: throw error if encryption fails instead of storing plaintext
- prevent duplicate warnings with hasWarnedAboutPlaintext flag

* fix(electron): add remaining review fixes

- Add Windows ARM64 architecture support
- Add IPC input validation with config key whitelist
- Add server.js existence check before starting Next.js server
- Make afterPack throw error on missing directories
- Add workflow permissions for release job

---------

Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

electron.d.ts

@@ -0,0 +1,74 @@
+/**
+ * Type declarations for Electron API exposed via preload script
+ */
+
+/** Configuration preset interface */
+interface ConfigPreset {
+    id: string
+    name: string
+    createdAt: number
+    updatedAt: number
+    config: {
+        AI_PROVIDER?: string
+        AI_MODEL?: string
+        AI_API_KEY?: string
+        AI_BASE_URL?: string
+        TEMPERATURE?: string
+        [key: string]: string | undefined
+    }
+}
+
+/** Result of applying a preset */
+interface ApplyPresetResult {
+    success: boolean
+    error?: string
+    env?: Record<string, string>
+}
+
+declare global {
+    interface Window {
+        /** Main window Electron API */
+        electronAPI?: {
+            /** Current platform (darwin, win32, linux) */
+            platform: NodeJS.Platform
+            /** Whether running in Electron environment */
+            isElectron: boolean
+            /** Get application version */
+            getVersion: () => Promise<string>
+            /** Minimize the window */
+            minimize: () => void
+            /** Maximize/restore the window */
+            maximize: () => void
+            /** Close the window */
+            close: () => void
+            /** Open file dialog and return file path */
+            openFile: () => Promise<string | null>
+            /** Save data to file via save dialog */
+            saveFile: (data: string) => Promise<boolean>
+        }
+
+        /** Settings window Electron API */
+        settingsAPI?: {
+            /** Get all configuration presets */
+            getPresets: () => Promise<ConfigPreset[]>
+            /** Get current preset ID */
+            getCurrentPresetId: () => Promise<string | null>
+            /** Get current preset */
+            getCurrentPreset: () => Promise<ConfigPreset | null>
+            /** Save (create or update) a preset */
+            savePreset: (preset: {
+                id?: string
+                name: string
+                config: Record<string, string | undefined>
+            }) => Promise<ConfigPreset>
+            /** Delete a preset */
+            deletePreset: (id: string) => Promise<boolean>
+            /** Apply a preset (sets environment variables and restarts server) */
+            applyPreset: (id: string) => Promise<ApplyPresetResult>
+            /** Close settings window */
+            close: () => void
+        }
+    }
+}
+
+export { ConfigPreset, ApplyPresetResult }