fix(discord-midnight): improve channel text contrast and accent color mappings

[the-daonm]

This pull request resolves contrast and color mapping issues in the discord-midnight community template when rendered with different color palettes (e.g. Gruvbox Material).

Changes Made

1. Text Contrast Fix (--text-4, --text-5)

• Issue: The template previously mapped channel list text/icons (--text-4) and muted chats/timestamps (--text-5) directly to colors.outline and colors.outline_variant. In dark mode, these resolve to very dark grey/near-black border colors, making the channel list text and timestamps completely unreadable.
• Fix: Replaced outline mappings with custom HSL/RGB color mixes:
  • --text-4 mixes 65% of the primary foreground (on_surface) with 35% outline, creating a legible cream-grey.
  • --text-5 mixes 40% foreground with 60% outline, producing a clean, muted, yet readable gray.
• This logic matches the robust mixes implemented in other templates like discord-system24 and works correctly for both light and dark shell modes.

2. Accent Mappings Fix (--accent-2, --accent-4)

• Issue: --accent-2 (small accent elements, such as chosen/selected channel indicators) was mapped to a dark container background color (primary_container), which was invisible on dark backgrounds. --accent-4 (hovered accent buttons) was mapped to a light text color (on_secondary_container), causing harsh brightness inconsistencies.
• Fix:
  • Re-mapped --accent-2 to the primary accent color (colors.primary), keeping active channel selections highlighted in the theme's primary accent color (e.g. Gruvbox green).
  • Re-mapped --accent-4 to a 80% secondary accent mix, creating a smooth and cohesive color shift on hover.

Type of Change

• Bug fix

How Has This Been Tested?

• Generated and loaded the theme (noctalia.theme.css) locally on Vesktop using the Gruvbox Material palette (both dark and light modes).
• Verified that channel list names, icons, muted channels, active channels, and hovered buttons are fully legible and cohesive.

[notiant]

I think normal text also has a bad contrast in dark mode. Maybe change text-3 to color-mix(in srgb, {{colors.on_surface.default.hex}} 85%, {{colors.outline.default.hex}}) as well?