feat(electron): add main process, preload, store, protocol, and type definitions

- Add ElectronAPI type definitions and runtime contract (isElectron guard)
- Add electron-store with backend connection data model
- Add centralized API base URL utility (api-base.ts)
- Implement app:// custom protocol with API proxy
- Implement preload script with full contextBridge API
- Complete main process: BrowserWindow config, IPC handlers, window controls
- Register app:// scheme as privileged for secure renderer access

dashboard/src/types/electron.d.ts

@@ -0,0 +1,95 @@
+/**
+ * Electron API type definitions
+ * Declares Window.electronAPI and globalThis.__RUNTIME__ for frontend use
+ */
+
+import type { RuntimeInfo } from '@/lib/runtime'
+
+/**
+ * Backend connection configuration
+ */
+export interface BackendConnection {
+  /** Unique identifier */
+  id: string
+  /** Display name */
+  name: string
+  /** Connection URL */
+  url: string
+  /** Whether this is the default backend */
+  isDefault: boolean
+  /** Last connection timestamp */
+  lastConnected?: number
+}
+
+/**
+ * Electron IPC API exposed to renderer process
+ * All methods communicate via IPC bridges to main process
+ */
+export interface ElectronAPI {
+  // Window control
+  /** Minimize the application window */
+  minimizeWindow(): void
+  /** Maximize the application window */
+  maximizeWindow(): void
+  /** Close the application window */
+  closeWindow(): void
+  /** Check if window is currently maximized */
+  isMaximized(): Promise<boolean>
+
+  // Window event listeners
+  /** Register callback for window maximized event */
+  onWindowMaximized(callback: () => void): () => void
+  /** Register callback for window unmaximized event */
+  onWindowUnmaximized(callback: () => void): () => void
+
+  // Backend management
+  /** Get list of all configured backends */
+  getBackends(): Promise<BackendConnection[]>
+  /** Add a new backend connection */
+  addBackend(conn: Omit<BackendConnection, 'id'>): Promise<BackendConnection>
+  /** Update an existing backend configuration */
+  updateBackend(id: string, patch: Partial<BackendConnection>): Promise<void>
+  /** Remove a backend by ID */
+  removeBackend(id: string): Promise<void>
+  /** Set the active backend */
+  setActiveBackend(id: string): Promise<void>
+  /** Get the currently active backend */
+  getActiveBackend(): Promise<BackendConnection | null>
+  /** Get the active backend's URL for API requests */
+  getActiveBackendUrl(): Promise<string | null>
+
+  // Application state
+  /** Mark that first-launch setup has been completed */
+  markFirstLaunchComplete(): Promise<void>
+  /** Check if this is the first launch */
+  isFirstLaunch(): Promise<boolean>
+  /** Get application version */
+  getAppVersion(): Promise<string>
+
+  // Backend event listener
+  /** Register callback for backend change events */
+  onBackendChanged(callback: (backend: BackendConnection | null) => void): () => void
+
+  // Platform detection
+  /** Get platform identifier (darwin, win32, linux) */
+  getPlatform(): string
+}
+
+// Extend Window interface to include electronAPI
+declare global {
+  interface Window {
+    /** Electron API bridge for main process communication */
+    electronAPI?: ElectronAPI
+  }
+
+  /**
+   * Global runtime information
+   * Set by Electron preload, undefined in browser
+   */
+  namespace globalThis {
+    var __RUNTIME__: RuntimeInfo | undefined
+  }
+}
+
+// Ensure this file is treated as a module
+export {}