design(icon): replace ornate badge with clean white silhouette

Switch the app icon to a single-path white-filled clock so it works in
every Nextcloud theme: white in dark headers, inverted to black in
light headers via --background-image-invert-if-bright. Drops the green
compliance shield that turned to noise at 20px.

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

Author: aSoftwareByDesignRepository