fix: add configurable terminal font family

[BearHuddleston]

Summary

Make the embedded terminal font configurable from Settings so users can explicitly choose a Nerd Font such as FiraCode Nerd Font Mono, while keeping fallback composition and updating open terminals when the preference changes.

Why

The terminal still defaulted to a generic Menlo/Monaco/Courier stack, so installing a Nerd Font alone was not enough to make icon-heavy TUIs render with the intended font. Instead of auto-picking a detected font, this change makes the preference explicit and user-controlled.

What changed

• Added a shared terminal font helper that composes a single requested family with the existing fallback stack.
• Updated the xterm terminal view to resolve terminalFontFamily from prefs and react to pref:changed so open terminals pick up the new font immediately.
• Broadcast preference changes to all webContents and exposed onPrefChanged in the universal preload API.
• Added a Terminal font family field in Settings with common suggestions and reset behavior.
• Added focused tests for terminal font resolution and duplicate suppression.

Validation

• bun test packages/shared/src/terminal-font.test.ts
• bun x tsc --noEmit --pretty false

Notes

• This does not install fonts for the user. The chosen font still has to be installed where the embedded Chromium renderer can see it.
• Single-family entries like FiraCode Nerd Font Mono are expanded with the built-in fallback stack automatically.

Video

2026-04-07.21-43-57.mp4

[BearHuddleston]

@yiliushenburke Ready 🐻

[theblondealex]

looks pretty good to me

[yiliush]

Thx @BearHuddleston (and @theblondealex)! Taking a look shortly