fix(chatelet): don't offer a check-in that can't fit a minimum stay

The stay picker disabled only occupied nights when choosing a check-in, so
a free day with an occupied night closer than min_nights was still
selectable — e.g. min 2 nights with the night after next booked. Picking it
left every later day disabled (no legal check-out), so reka's only move was
an earlier day, which it silently swapped into the range: the guest picks a
date and the calendar 'jumps backwards'. Disable such a day up front: a
check-in is valid only if the minimum stay fits before the next occupied
night and within the loaded window.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/modules/chatelet/components/StayDatePicker.vue

@@ -106,8 +106,19 @@ function isDateDisabled(d: DateValue): boolean {
   if (y < todayYmd) return true
   const start = activeStart.value
   if (!start) {
-    // Picking a check-in: occupied nights are out; everything else is fair.
+    // Picking a check-in. An occupied night is out — except a committed
-    return props.nightSet.has(y) && !(bothSet.value && y === props.checkOut)
+    // check-out that landed on one, which must stay rendered as selected.
+    if (props.nightSet.has(y)) return !(bothSet.value && y === props.checkOut)
+    // A free day is only a valid check-in if a minimum stay fits before the
+    // next occupied night AND within the loaded window. Otherwise reka would
+    // offer it, then strand the guest with no reachable check-out (every
+    // later day disabled), so the only click left is an earlier day, which
+    // reka silently swaps into the range. Disable it up front instead.
+    const minCheckOut = addDays(y, props.minNights)
+    const nextOccupied = nextUnavailableOnOrAfter(props.nights, y)
+    if (nextOccupied && nextOccupied < minCheckOut) return true
+    if (props.maxDate && minCheckOut > props.maxDate) return true
+    return false
   }
   if (y === start) return false
   if (y > start) {