desktop: fix theme palette bugs, light-mode contrast failures, and token typos in packages/ui #50500

Description

Scope Note: This issue covers the Desktop app themes in packages/ui.
Companion TUI themes in packages/tui are tracked in #50523.

While testing light themes in OpenCode Desktop, we identified several broken light-mode palettes, token typos, and a contrast calculation issue in packages/ui:

1. Light Mode Palette Breakages

• catppuccin.json (Latte): light.palette.neutral uses Mocha Rosewater (#f5e0dc) instead of official Latte Base (#eff1f5). Because neutral seeds the entire neutral scale, the app displays with a heavy pink tint in light mode.
• catppuccin-frappe.json & catppuccin-macchiato.json: Both duplicate dark-flavor tokens into light mode, producing washed-out, unreadable body text (< 2.1:1 contrast).
• kanagawa.json: Light overrides copy dark Wave tokens onto the Lotus background (#f4ede3), making strings and constants unreadable (< 2:1 contrast).
• matrix.json: syntax-type uses neon yellow (#e6ff57) on light background (#f0f5ed), rendering type text virtually invisible (~1:1 contrast).

2. Concrete Token and Formula Typos

• oc-2.json: Line 28 defines "icon-weak-base": "C7C7C7" without the # prefix. The resulting invalid CSS variable breaks icon shadows and logo fills.
• catppuccin-frappe.json: Uses #8da4e2 instead of Frappé Blue (#8caaee) and #949cb8 instead of Overlay 2 (#949cbb).
• color.ts: contrastRatio() uses 0.587 instead of the standard ITU-R BT.709 coefficient 0.7152 for green luminance, calculating black-on-white as 18.4:1 instead of 21:1.

3. Question for Maintainers: Dark-Only Upstream Themes

11 bundled themes (amoled, aura, cobalt2, dracula, matrix, monokai, onedarkpro, shadesofpurple, synthwave84, vesper, zenburn) have no official upstream light palette.
Current synthetic light modes produce mixed results (for example, invisible syntax in Matrix).

Would maintainers prefer:

1. Locking these themes to dark mode only (falling back to OpenCode light if the user selects light mode)?
2. Keeping calibrated companion light palettes for them?

Steps to Reproduce

1. Open OpenCode Desktop Settings -> Appearance and set Color Scheme to Light.
2. Select Catppuccin to observe the pink background wash.
3. Select Catppuccin Frappe, Kanagawa, or Matrix to observe unreadable text contrast.

Screenshots

Before (Catppuccin Light pink wash):

After (Fixed Catppuccin Latte Base #eff1f5):

Operating System

Windows 11 / Linux