feat: 15-minute rental slots + compact calendar cell display

- Rental bookings now use minutes since midnight (start_hour/end_hour
  store e.g. 495 for 8:15, 570 for 9:30) — DB migration 017
- Buffer applied in exact minutes (no hour ceiling): 15min buffer after
  9:00 booking → next slot available at 9:15
- Calendar cell: removed working-hours line (8:00–22:00), now shows
  colored dot + compact time per booking (8–10, 8:15–9:15)
- Time selects show HH:MM format for 15-min intervals

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/calendar/BookingCalendar.tsx

@@ -696,26 +696,21 @@ export function BookingCalendar({ rooms, bookings, slug, onBookingCreate, onBook
                           ) : dayBookings.length > 0 ? (
                             /* Hourly bookings — squares + times */
                             <div className="absolute inset-x-1 top-1.5 flex flex-col gap-0.5">
-                              {/* One colored square per booking */}
-                              <div className="flex gap-0.5 flex-wrap">
-                                {dayBookings.map(b => (
-                                  <div
-                                    key={b.id}
-                                    className={cn('w-3 h-3 rounded-[3px]', obj.color)}
-                                    title={`${b.guestName} · ${b.startHour}:00–${b.endHour}:00`}
-                                  />
-                                ))}
-                              </div>
-                              {/* Working hours range */}
-                              <span className="text-[9px] text-slate-400 dark:text-slate-500 leading-none">
-                                {obj.openHour}:00–{obj.closeHour}:00
-                              </span>
-                              {/* Booked time slots */}
-                              {dayBookings.map(b => (
-                                <span key={b.id} className="text-[9px] text-slate-600 dark:text-slate-300 font-medium leading-none">
-                                  {b.startHour}–{b.endHour}
-                                </span>
-                              ))}
+                                  {/* One colored dot per booking + its time */}
+                              {dayBookings.map(b => {
+                                const fmtT = (min: number) => {
+                                  const h = Math.floor(min / 60), m = min % 60
+                                  return m === 0 ? `${h}` : `${h}:${String(m).padStart(2,'0')}`
+                                }
+                                return (
+                                  <div key={b.id} className="flex items-center gap-0.5">
+                                    <div className={cn('w-2.5 h-2.5 rounded-[3px] shrink-0', obj.color)} />
+                                    <span className="text-[9px] text-slate-700 dark:text-slate-200 font-medium leading-none truncate">
+                                      {fmtT(b.startHour)}–{fmtT(b.endHour)}
+                                    </span>
+                                  </div>
+                                )
+                              })}
                             </div>
                           ) : (
                             /* Empty — show "+" hint on hover */