chore: enhance the gzip and cacheable handling of static files

Add SVG and ICO to cacheable files.
Emit robots.txt directly.
Recognize WOFF2 (font) files as assets (so the get the immutable treatment)
Pre-gzip the entire /static/ directory (not just /static/assets/) and include SVG, ICO, and HTML files
Ensure fonts.css is processed by vite/rollup so that the preload and css reference the same immutable files (which get long-cached with hashes)
Add CircularXXWeb-Black to the preload list as it is used in the hot-path.
Handle system-driven color-scheme changes from dark to light correctly.

Makefile

@@ -63,14 +63,17 @@ build_dev_test: build_test2json build_gotestsum
 
 frontend:
 	cd ui && npm ci && npm run build:device && \
-	find ../static/assets \
+	find ../static/ \
 		-type f \
 		\( -name '*.js' \
 		-o -name '*.css' \
+		-o -name '*.html' \
+		-o -name '*.ico' \
 		-o -name '*.png' \
 		-o -name '*.jpg' \
 		-o -name '*.jpeg' \
 		-o -name '*.gif' \
+		-o -name '*.svg' \
 		-o -name '*.webp' \
 		-o -name '*.woff2' \
 		\) \