Add the mobile swap sheet to the Draft board

Tapping a day tile puts it in the swapping state and opens a bottom sheet
segmented "Quest log · N | Regulars · N". Choosing a dinner swaps the day
optimistically with PUT /api/v1/plans/{weekStart}/days/{date}, landing the
server's plan on success and rolling the day back with an ErrorBanner and
Retry on failure. Dinners already this week are marked and not selectable.

Maestro task f231813c-992e-4a3b-a1a4-868cbad47415.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/discover/QuestLogSheet.tsx

@@ -20,7 +20,7 @@ export type QuestLogSheetProps = {
 
 // details is a Quest-log dinner's "difficulty · minutes" line, or null when
 // neither is known.
-function details(dinner: QuestLogDinner): string | null {
+export function details(dinner: QuestLogDinner): string | null {
   const parts = [
     dinner.difficulty !== null && DIFFICULTY_LABEL[dinner.difficulty],
     dinner.minutes_total !== null && `${dinner.minutes_total} min`,