Add Technical Kiwi website with Go, templ, and HTMX.

Single-page site with gallery by album and event, contact form over SMTP,
Docker dev/prod setup, and on-server image derivatives. Gallery photos stay
local (app/images/ is gitignored).

Co-authored-by: Cursor <cursoragent@cursor.com>

app/internal/gallery/hero.go

@@ -0,0 +1,34 @@
+package gallery
+
+import (
+	"os"
+	"strings"
+)
+
+const defaultHeroRel = "connectionmachine/20220723_231556.jpg"
+
+// HeroRelPath returns the configured hero image path relative to images/.
+func HeroRelPath() string {
+	if p := strings.TrimSpace(os.Getenv("HERO_IMAGE")); p != "" {
+		return filepathToSlash(p)
+	}
+	return defaultHeroRel
+}
+
+// SelectHero picks the homepage hero from the gallery list.
+func SelectHero(images []Image) (Image, bool) {
+	want := HeroRelPath()
+	for _, img := range images {
+		if img.RelPath == want {
+			return img, true
+		}
+	}
+	if len(images) > 0 {
+		return images[0], true
+	}
+	return Image{}, false
+}
+
+func filepathToSlash(p string) string {
+	return strings.ReplaceAll(p, "\\", "/")
+}