Mobile DaysView: day filter bar (✓/✗/?) + multi-day spans + holes

Deferred from Phase 3 mobile redesign (T24). DaysView ships with day-grouped sections and dayPosition sort, but the following are tracked here:

1. Filter bar: ✓/✗/? toggle above the section list — filters options by status (chosen / rejected / undecided). This is the 'Deciding/Picked two-views' concept (batch-locked decision flow).
2. Multi-day spans: options with startOffset != endOffset should render a span indicator across the days they cover.
3. Holes: days in the range that have no options should still appear as empty day sections (with placeholder text) rather than being skipped entirely.

Reference: apps/mobile/components/views/DaysView.tsx