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>

docs/development.md

@@ -24,7 +24,8 @@ scripts/e2e.sh        end-to-end test with real DHCP clients in Docker
 scripts/mkdeb.sh      the Debian packages (make deb)
 scripts/logo.py       the web UI's logo from artwork/logo.svg
 scripts/optionsdoc.py docs/options.md from the option catalog
-artwork/logo.svg      the logo's master
+scripts/banner.py     the README's banner from the web UI's logo and wordmark
+artwork/logo.svg      the logo's master; artwork/banner.svg the README's banner
 ```
 
 [design.md](design.md) describes how the pieces fit.
@@ -83,8 +84,11 @@ same helpers as Jarl's:
 
 The logo's master is `artwork/logo.svg`; `scripts/logo.py` writes
 `assets/logo.svg` (the favicon) and `assets/logo.js` (drawn inline by
-`brand.js`). The STEWARD wordmark is drawn by `wordmark()` in `brand.js`,
-in the letters of Jarl's wordmark.
+`brand.js`), and then runs `scripts/banner.py`. The STEWARD wordmark is
+drawn by `wordmark()` in `brand.js`, in the letters of Jarl's wordmark.
+`artwork/banner.svg`, the README's banner, is the login page's logo and
+wordmark, generated by `scripts/banner.py`. It draws the rule with the same
+numbers as `brand.js`, so change both together.
 
 ## Conventions