[Feature]: Add colorblind-friendly diff colors setting #1533

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/web

Problem or use case

I'm red-green colorblind, and the diff panel is basically unusable for me. The red/green coloring for additions and deletions blends together so I can't tell what was added vs removed without reading each line carefully.

Proposed solution

Add a "Colorblind-friendly diff colors" toggle in Settings > General that swaps the diff panel palette from red/green to blue/orange. Blue and orange are distinguishable across all common forms of color vision deficiency (deuteranopia, protanopia, tritanopia).

Why this matters

About 8% of males have some form of red-green color blindness. Anyone in that group currently can't use the diff panel effectively. A simple opt-in toggle fixes it with no impact on anyone else.

Smallest useful scope

A single boolean client setting that swaps the CSS color variables on the diff panel. Four files, ~60 lines.

Alternatives considered

Custom themes (#1279) would technically solve this too, but that's a much bigger scope. A focused toggle is simpler, ships faster, and directly targets the accessibility problem.

Risks or tradeoffs

None significant. It's opt-in (default off), client-side only, and uses hardcoded oklch values that don't depend on any theme variables.

Examples or references

VS Code, GitHub, and most modern diff tools offer a similar colorblind mode or high-contrast theme for diffs.

Contribution

• I would be open to helping implement this.