style(planning): implement Month/Week/Day calendar views from sketch 005
- Replace 14-day agenda list with three-view calendar (month/week/day)
- Add PlanningCalendar, CalendarDay, CalendarTimeEvent, MiniCalDay data structs
- Add BuildMonthCalendar, BuildWeekCalendar, BuildDayCalendar builder helpers
- Add MondayOf, PlanningMonthURL, PlanningWeekURL, PlanningDayURL URL helpers
- Handler now parses ?view=month|week|day with matching date params
- Month view: 7-col grid with event chips using tablo color via color-mix()
- Week/Day view: split layout with mini-month panel and hour timeline (07-20)
- Timeline events positioned via TopPx/HeightPx from start_time microseconds
- Append all calendar CSS to app.css (view-toggle, cal-grid, tl-* classes)
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