⚡️ Feature Request: Add CJK font fallback and a font customization option (family / size)

[seanlees]

Feature Description

Add CJK-capable font fallback, and expose font settings (family / size) in the UI.

Arcane is fully translated into Chinese, but the bundled fonts do not cover
Han characters, so Chinese text renders with the OS fallback font. The goal
is (1) readable CJK text out of the box, and (2) a way for users to adjust
typography to their own environment.

Problem It Solves

1. CJK text falls back to the OS font

In _app/immutable/assets/0.*.css, Arcane defines only two font families:

• Montserrat Variable
• Geist Mono Variable

Their unicode-range covers Latin, Cyrillic, Vietnamese and some symbols.
Searching the entire stylesheet for U+4E00 (start of the CJK block)
returns 0 matches, so no bundled font can render Han characters.

As a consequence, Chinese text is rendered by the system fallback font
(e.g. Microsoft YaHei on Windows), which only ships Regular and Bold:

• intermediate weights get synthesized, so strokes look blurred
• baseline and weight mismatch when Latin and CJK appear on the same line
• most visible at small sizes (text-xs, text-sm)

This is easy to observe on the login page with zh-CN.

2. No way to adjust typography

Users cannot change the interface font family or base font size. This
matters beyond CJK:

• users on HiDPI / large displays who need a larger base size
• users who prefer a different font than Montserrat
• log- and code-heavy views where a mono font is preferable
• users who need a CJK font of their choosing instead of the OS default

Proposed Solution

1. Ship a subsetted CJK font (e.g. Noto Sans SC split by unicode-range)
   and append it to the font stack, so CJK glyphs resolve to a real font
   instead of an OS fallback.

2. Add a "Typography" section to settings exposing:

   • interface font family
   • monospace font family
   • base font size (and optionally base weight)

   These map cleanly onto the CSS variables already present in the
   stylesheet: --default-font-family and --default-mono-font-family.
   Values could be applied as inline CSS variables on :root, so no
   rebuild is needed and users can pick any locally installed font.

Alternatives Considered

• Do nothing. Users on Linux/Windows keep a blurred CJK UI; the
  translation is complete but visually inconsistent.

• Inject CSS via a reverse proxy (sub_filter). Works, but requires
  running an extra proxy in front of the container. It is fragile:
  sub_filter needs Accept-Encoding disabled, and the injected rules
  depend on internal class names that change between releases.

• Browser extension (e.g. Stylus). Simple and effective, but per-device,
  per-browser, and unsuitable for shared/team deployments.

• A full custom font loader in the UI. Considered, but heavier than
  needed — the two points above cover the actual use cases.

Additional Context

• Arcane: v2.17.1 (ghcr.io/getarcaneapp/manager:latest)
• Chrome on Windows, locale zh-CN
• Screenshot of the login page attached: Chinese text looks noticeably
  softer/blurrier than the surrounding Latin text, most obvious in the
  subtitle under "欢迎回来" and on the login button label.

Would you be willing to work on this feature?

• Yes, I'd like to implement this feature
• I could help with parts of this feature
• No, I'm just suggesting the feature