feat: implement CSS sprite system for image optimization

Reduces HTTP requests from 44+ individual images to 3 sprite sheets
(~93% reduction). Includes Go sprite generator tool, CSS classes,
template integration, and E2E tests.

- Add cmd/sprites/main.go for sprite generation (60x60px + 120x120px @2x)
- Add _sprites.css with responsive sizing and retina support
- Update templates to use sprites with logoIndex fallback
- Add Makefile targets: sprites, sprites-clean
- Add 9-test E2E suite for sprite functionality
- Add doc/22-SPRITES.md with usage documentation

go.mod

@@ -7,17 +7,14 @@ require (
 	github.com/chromedp/chromedp v0.14.2
 	github.com/go-git/go-git/v5 v5.16.4
 	github.com/joho/godotenv v1.5.1
+	golang.org/x/image v0.33.0
+	golang.org/x/text v0.31.0
 )
 
 require (
 	dario.cat/mergo v1.0.0 // indirect
-	github.com/Masterminds/semver v1.4.2 // indirect
-	github.com/Masterminds/sprig v2.16.0+incompatible // indirect
 	github.com/Microsoft/go-winio v0.6.2 // indirect
 	github.com/ProtonMail/go-crypto v1.1.6 // indirect
-	github.com/PuerkitoBio/goquery v1.5.0 // indirect
-	github.com/andybalholm/cascadia v1.0.0 // indirect
-	github.com/aokoli/goutils v1.0.1 // indirect
 	github.com/chromedp/sysutil v1.1.0 // indirect
 	github.com/cloudflare/circl v1.6.1 // indirect
 	github.com/cyphar/filepath-securejoin v0.4.1 // indirect
@@ -29,24 +26,11 @@ require (
 	github.com/gobwas/pool v0.2.1 // indirect
 	github.com/gobwas/ws v1.4.0 // indirect
 	github.com/golang/groupcache v0.0.0-20241129210726-2c02b8208cf8 // indirect
-	github.com/google/uuid v1.0.0 // indirect
-	github.com/gorilla/css v1.0.0 // indirect
-	github.com/huandu/xstrings v1.2.0 // indirect
-	github.com/imdario/mergo v0.3.6 // indirect
-	github.com/jaytaylor/html2text v0.0.0-20180606194806-57d518f124b0 // indirect
 	github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99 // indirect
 	github.com/kevinburke/ssh_config v1.2.0 // indirect
-	github.com/matcornic/hermes/v2 v2.1.0 // indirect
-	github.com/mattn/go-runewidth v0.0.3 // indirect
-	github.com/olekukonko/tablewriter v0.0.1 // indirect
 	github.com/pjbgf/sha1cd v0.3.2 // indirect
-	github.com/russross/blackfriday/v2 v2.0.1 // indirect
 	github.com/sergi/go-diff v1.3.2-0.20230802210424-5b0b94c5c0d3 // indirect
-	github.com/shurcooL/sanitized_anchor_name v1.0.0 // indirect
 	github.com/skeema/knownhosts v1.3.1 // indirect
-	github.com/ssor/bom v0.0.0-20170718123548-6386211fdfcf // indirect
-	github.com/vanng822/css v0.0.0-20190504095207-a21e860bcd04 // indirect
-	github.com/vanng822/go-premailer v0.0.0-20191214114701-be27abe028fe // indirect
 	github.com/xanzy/ssh-agent v0.3.3 // indirect
 	golang.org/x/crypto v0.37.0 // indirect
 	golang.org/x/net v0.39.0 // indirect