fix(readme): show Wednesday logo in light mode via picture tag

The remote logo at mobile.wednesday.is/logos/wednesday-logo.svg uses
fill="white" for all paths — designed for dark backgrounds. On light
mode the white logo renders invisibly on the white GitHub page.

Wrap the logo in <picture> with prefers-color-scheme branching:

- Dark mode → use the remote white-fill SVG (visible on dark page)
- Light mode → use the local src/assets/wednesday-logo.svg
              (dark fill, designed for light page)

Each theme now gets a logo designed for it, no white-card workaround
needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Ganeshship

README.md

@@ -24,7 +24,7 @@
 
 <sub><b>BUILT BY</b></sub>
 
-<a href="https://mobile.wednesday.is/hire-ai-native-mobile-squad"><img src="https://mobile.wednesday.is/logos/wednesday-logo.svg" alt="Wednesday Solutions" height="104" /></a>
+<a href="https://mobile.wednesday.is/hire-ai-native-mobile-squad"><picture><source media="(prefers-color-scheme: dark)" srcset="https://mobile.wednesday.is/logos/wednesday-logo.svg" /><img src="src/assets/wednesday-logo.svg" alt="Wednesday Solutions" height="104" /></picture></a>
 
 </div>