style: remove hyphens from compound adjectives in comments and messages

Remove hyphens from compound adjectives such as "logged-in", "one-time", "password-protected", "full-height", "multi-file", and "S3-compatible" in comments, test error messages, and UI labels to improve readability and consistency.

backend/libs/handlers/ogimage.go

@@ -552,7 +552,7 @@ func collageGrid(n int) (cols, rows int) {
 }
 
 // drawCover scales src to completely fill dst, cropping the overflow (centred),
-// preserving aspect ratio — the CSS object-fit: cover equivalent.
+// preserving aspect ratio. the CSS object-fit: cover equivalent.
 func drawCover(dst *image.RGBA, cell image.Rectangle, src image.Image) {
 	b := src.Bounds()
 	iw, ih := b.Dx(), b.Dy()