feat: add defaultValue support for showFontPicker in puter app environment

[smz202000]

Description

This PR adds support for the defaultValue option in puter.ui.showFontPicker(), for consistency with showColorPicker() which already supports defaultValue.

When calling showFontPicker from a Puter app, passing defaultValue as an option would not pre-select the specified font because:

1. The IPC handler did not map defaultValue to default before passing to the desktop UI
2. The desktop UI window (UIWindowFontPicker) only checked options.default
3. The web fallback only checked defaultFont and default

Changes

• UI.js (web fallback): Added opts.defaultValue to the font resolution chain
• IPC.js (app environment): Map defaultValue to default before calling UIWindowFontPicker
• UIWindowFontPicker.js (desktop UI): Check defaultValue alongside default when highlighting the active font
• ui.d.ts (types): Added defaultValue to FontPickerOptions interface

Related Issue

Closes #2896

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[Salazareo]

@smz202000 could you sign the CLA