Use custom icon from assets/icons/custom/ for app and tray icons

[Copilot]

Updated icon generation scripts to use the custom icon file in assets/icons/custom/ instead of programmatically generating icons.

Changes

• generate-app-icons.js: Replaced gradient/rounded-corner generation with loading from custom PNG file
• generate-tray-icon.js: Replaced SVG-based generation with custom PNG file
• Added directory existence validation and alphabetical file selection for predictable behavior

Both scripts now automatically detect and use the first PNG file (alphabetically sorted) from assets/icons/custom/ to generate all platform-specific icon formats (macOS .icns, Windows .ico, Linux .png, and tray icon).

// Find and load custom icon
const customIconFiles = fs.readdirSync(customIconDir)
  .filter(file => file.toLowerCase().endsWith('.png'))
  .sort();

const customIconPath = path.join(customIconDir, customIconFiles[0]);
const image = await Jimp.read(customIconPath);

Original prompt

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This section details on the original issue you should resolve

<issue_title>Use custom app icon</issue_title>
<issue_description>Update the generate generate-app-icons and generate-tray-icons to use the source icon file in assets/icons/custom/</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Use custom app icon #12

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