fix: use rounded app AO icon in Electron

[nikhilachale]

Description

This PR updates the Electron app icon handling so the app uses our AO icon consistently instead of showing the default Electron icon or a hard square icon in the macOS Dock.

Changes

Code Updates

• Added macOS runtime Dock icon support in frontend/src/main.ts
  • Implemented app.dock.setIcon(...) to set the Dock icon at runtime
  • Ensures the correct icon displays in the macOS Dock during development and packaged builds

Icon Asset Updates

• Reused existing windowIconPath() resolution

  • Dev mode: loads frontend/assets/icon.png
  • Packaged builds: loads from process.resourcesPath/icon.png
  • Maintains consistency across build modes

• Updated icon assets with rounded corners

  • Modified frontend/assets/icon.png to have transparent corners
  • Replaced opaque square background with transparent pixels
  • Regenerated platform-specific icon assets:
    • frontend/assets/icon.ico (Windows)
    • frontend/assets/icon.icns (macOS, if applicable)

Why This Change?

Problem

• BrowserWindow({ icon }) works for Windows/Linux window and taskbar icons
• macOS ignores BrowserWindow.icon for the Dock icon display
• Without explicit runtime configuration, the Dock showed:
  • Electron's default icon
  • Hard square appearance (opaque background)
  • Stale/unrounded icon during development

Solution

1. macOS Dock requires app.dock.setIcon(...) at runtime

   • The Dock icon is a separate entity from the window icon on macOS
   • Must be set after app.whenReady() and before window creation

2. Transparent corners for proper appearance

   • PNG corners are now transparent instead of opaque
   • Provides the rounded, polished look expected on modern macOS

3. Consistent icon resolution

   • Reuses existing windowIconPath() logic
   • Ensures dev and packaged builds both use the correct asset

Screenshots / Evidence

Closes #430