feat(api): keyless unavailable-ranges feed for the guest calendar

GET /api/v1/public/rooms/{id}/unavailable?start=&end= and its RPC twin
chatelet_room_unavailable return the nights a guest cannot book over a
window (default today → +365 d, capped at 400 d): occupying bookings —
live holds included, so the feed always agrees with POST /availability —
and manual blocks, clipped, sorted and coalesced into anonymous half-open
spans. Adjacent spans merge on purpose so a guest cannot tell where one
occupant's dates end and the next begin, nor a block from a stay.

is_available now uses the OCCUPYING_STATUSES constant it was inlining.

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

models.py

@@ -231,6 +231,27 @@ class AvailabilityQuery(BaseModel):
     check_out: str  # YYYY-MM-DD exclusive
 
 
+class DateRange(BaseModel):
+    """Half-open [start, end) span of nights, YYYY-MM-DD. `end` is the morning
+    the room frees up — a guest may check in on that day."""
+
+    start: str
+    end: str
+
+
+class UnavailableRanges(BaseModel):
+    """Everything a guest calendar needs to grey out nights for one room
+    over a window: bookings that still occupy the room (incl. live unpaid
+    holds, so this always agrees with `POST /availability`) and manual
+    blocks, merged into indistinguishable date spans — a guest can't tell a
+    block from another guest's stay."""
+
+    room_id: str
+    start: str
+    end: str
+    ranges: list[DateRange] = Field(default_factory=list)
+
+
 class AvailabilityResult(BaseModel):
     room_id: str
     check_in: str