fix(ui): update favicon dynamically based on app theme

[GuillaumeLecomte1]

Summary

The favicon did not switch between light and dark variants when toggling the app theme because it relied on OS prefers-color-scheme media query instead of the app-level theme state.

Changes

New files:

• icon-light.svg - favicon with fill=black
• icon-dark.svg - favicon with fill=white

Modified:

• WhitelabelingProvider.tsx - Added useTheme from next-themes and logic to select icon based on resolvedTheme. Custom faviconUrl still takes precedence.

Closes #4100

Greptile Summary

This PR adds two new SVG assets (icon-dark.svg with white fill, icon-light.svg with black fill) and updates WhitelabelingProvider to select the favicon based on resolvedTheme from next-themes, so the app-level theme toggle is respected instead of the OS media query.

• The faviconHref is computed before if (!config) return null, but the component still returns null while config loads, meaning the theme-aware favicon isn't rendered during the initial API call — the non-themed /icon.svg from _document.tsx shows until config resolves. The early return should be removed and optional chaining used throughout JSX so the favicon link renders immediately.

Confidence Score: 4/5

• The PR partially works — theme changes after load are handled correctly — but the fix doesn't apply during initial page load due to the early return guard.
• One P1 issue: the if (!config) return null guard prevents the theme-aware favicon from rendering before config resolves, meaning the feature only works after the first API call completes. This is a real behavioral gap in the fix.
• apps/dokploy/components/proprietary/whitelabeling/whitelabeling-provider.tsx

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