Add mobile terminal font selection

[ZacharyZcR]

Overview

Add mobile terminal font selection under Settings -> Customize Terminal so users can choose the terminal font family on iOS and Android.

• Added: terminal font family selection in mobile settings
• Updated: terminal customization persistence to save font family
• Fixed: terminal WebView screen CSS no longer hardcodes Caskaydia over the selected font
• Updated: stored terminal config loading to merge defaults with older saved configs

Changes Made

• Render the existing TERMINAL_FONTS options in the mobile Terminal Customization screen.
• Persist selected fontFamily through TerminalCustomizationContext.
• Preserve new default config fields when loading older stored mobile terminal settings.
• Apply the selected font family to .xterm-screen instead of overriding it with a fixed Caskaydia stack.
• Keep existing font size controls intact.

Related Issues

• Closes [FEATURE] font selection for mobile apps Support#546

Screenshots / Demos

Not included; this is a settings and terminal rendering change that should be verified on iOS/Android with an SSH session using Nerd Font glyphs.

Validation run locally:

• npx eslint app/contexts/TerminalCustomizationContext.tsx app/tabs/settings/TerminalCustomization.tsx passes.
• npx eslint app/contexts/TerminalCustomizationContext.tsx app/tabs/settings/TerminalCustomization.tsx app/tabs/sessions/terminal/Terminal.tsx passes with existing Terminal warnings only.
• npx prettier --check app/contexts/TerminalCustomizationContext.tsx app/tabs/settings/TerminalCustomization.tsx app/tabs/sessions/terminal/Terminal.tsx passes.
• git diff --check passes.
• npx tsc --noEmit still fails on existing repository-wide TypeScript errors outside this change.

Checklist

• Code follows project style guidelines
• Supports mobile and desktop UI/app (if applicable)
• I have read Contributing.md