docs: dark-mode Wednesday logo, bump size (#397)

The single SVG has a white backdrop rect baked in, so on GitHub dark mode the logo rendered as a white card. Add a transparent variant with white glyphs and wire it via <picture> + prefers-color-scheme. Bump height from 104 to 160.

Co-authored-by: User <user@Users-MacBook-Pro.local>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 3 people

README.md

@@ -25,7 +25,7 @@
 
 <sub><b>BUILT BY</b></sub>
 
-<a href="https://wednesday.is/?utm_source=github&utm_medium=offgrid-readme&utm_content=logo"><img src="src/assets/wednesday-logo.svg" alt="Wednesday Solutions" height="104" /></a>
+<a href="https://wednesday.is/?utm_source=github&utm_medium=offgrid-readme&utm_content=logo"><picture><source media="(prefers-color-scheme: dark)" srcset="src/assets/wednesday-logo-dark.svg" /><img src="src/assets/wednesday-logo.svg" alt="Wednesday Solutions" height="160" /></picture></a>
 
 </div>