Add a showHourLines preference (default off — the existing clean look). When on, the week and day timelines draw a faint outline-variant line at each hour boundary, sitting over the column background but beneath event blocks. The toggle is provided app-wide via LocalShowHourLines and applied through a reusable hourSeparatorLines() modifier. Closes #5 (Codeberg) Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>