Improve gallery video UX and add upload-to-publish media workflow.

Stage raw files in upload/, publish with make sync-media/publish, and polish the lightbox: autoplay, remembered volume, Escape to close, and image/video icons without poster or caption clutter.

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

app/templates/helpers.go

@@ -1,22 +1,7 @@
 package templates
 
-import (
-	"path/filepath"
-	"strings"
-	"time"
-)
+import "time"
 
 func currentYear() string {
 	return time.Now().Format("2006")
 }
-
-func videoMIME(filename string) string {
-	switch strings.ToLower(filepath.Ext(filename)) {
-	case ".webm":
-		return "video/webm"
-	case ".mov":
-		return "video/quicktime"
-	default:
-		return "video/mp4"
-	}
-}