[Bug]: provider badge initials are invisible on light accent colors

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. Open Settings → Providers and edit a provider instance (for example Codex).
2. Set a custom accent color to white #ffffff (any light color reproduces it).
3. Look at the provider icon in the sidebar, the model picker, or Settings → Usage.

Expected behavior

The account badge keeps its initials readable for every accent color. A light accent should get dark text, a dark accent should get light text.

Actual behavior

The badge always paints its initials in white (text-white in apps/web/src/components/chat/ProviderInstanceIcon.tsx), so with a white or light accent the initials disappear. In the screenshot below Codex has a white accent and shows no "CO", while Claude's orange accent still shows "CL".

The mobile badge has the same hardcoded white text in apps/mobile/src/components/ProviderIcon.tsx.

Impact

Cosmetic issue

Version or commit

0.0.40-nightly

Environment

macOS desktop app, dark theme

Screenshots, recordings, or supporting files

See the screenshot above.

Start with apps/web/src/components/chat/ProviderInstanceIcon.tsx and apps/mobile/src/components/ProviderIcon.tsx, focusing on the hardcoded text-white styling and how each badge receives its accent color. Reproduce the issue with a white or light accent in the provider settings, sidebar, model picker, and Usage views. Done means provider initials remain readable across light and dark accent colors on web and mobile.