README banner: the logo above the STEWARD wordmark

scripts/banner.py builds artwork/banner.svg from the web UI's logo and
wordmark, as Jarl's does; scripts/logo.py runs it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -1,4 +1,4 @@
-<p align="center"><img src="artwork/logo.svg" width="140" alt="Steward"></p>
+<p align="center"><img src="artwork/banner.svg" width="340" alt="Steward: a key whose bow is a crown with network nodes, above the STEWARD wordmark"></p>
 
 # Steward