Cockpit v1.7.7

Restores the established Dark preset appearance after the light-theme contrast fix.\n\n- Section headings such as TODAY and THIS MONTH are muted grey again.\n- Selected to-dos and calendar days use the former neutral-grey highlight again.\n- Light and Solarized Light retain their corrected high-contrast foreground/background pairs.\n- Adds focused harness and real-Joplin regression coverage for both Light and Dark.