Change accent colors from blue to dark green (light & dark modes)

[Copilot]

The app's accent color palette used blue throughout all interactive UI elements. This updates all accent colors to dark green across both light and dark themes.

Changes

frontend/style.css

• Light mode: #1976d2 → #2e7d32 (primary), #1565c0 → #1b5e20 (hover); button hover/active backgrounds and all shadow rgba values updated to green equivalents
• Dark mode: #64b5f6 → #66bb6a (primary), #42a5f5 → #4caf50 (hover); dark button backgrounds changed from indigo (#1a237e/#283593) to dark green (#1b5e20/#2e7d32); all shadow rgba values updated accordingly

/* Before */
--primary-color: #1976d2;   /* light */
--primary-color: #64b5f6;   /* dark */

/* After */
--primary-color: #2e7d32;   /* light — Material Green 800 */
--primary-color: #66bb6a;   /* dark — Material Green 400 */

Color choices follow Material Design green scale to ensure adequate contrast in both themes.

• Fixes Modifica los colores de acento en cada uno de los componentes de la aplicación; el color actual es azul, cámbialo de azul a verde oscuro. #28