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>

services.py

@@ -14,7 +14,7 @@ backend failure and surfaces as a generic error over RPC (logged server-side).
 
 import asyncio
 from collections import defaultdict
-from datetime import datetime, timedelta, timezone
+from datetime import date, datetime, timedelta, timezone
 
 from lnbits.core.services import create_invoice
 from lnbits.exceptions import InvoiceError
@@ -28,7 +28,9 @@ from .models import (
     BookingQuote,
     BookingRequestData,
     BookingStatus,
+    DateRange,
     RoomStatus,
+    UnavailableRanges,
 )
 
 # Per-room lock serializing the availability read + the `held` write, so two
@@ -59,6 +61,46 @@ async def to_sats(amount: float, currency: str) -> int:
     return await fiat_amount_as_satoshis(amount, currency)
 
 
+# A guest calendar asks for a year by default; cap the window so a bad client
+# can't make us scan and ship an unbounded span.
+DEFAULT_CALENDAR_DAYS = 365
+MAX_CALENDAR_DAYS = 400
+
+
+async def get_unavailable_ranges(
+    room_id: str, start: str | None = None, end: str | None = None
+) -> UnavailableRanges:
+    """Occupied/blocked nights for one active room over [start, end).
+    Defaults to today → +365 days (UTC dates)."""
+    room = await crud.get_room(room_id)
+    if not room or room.status != RoomStatus.active:
+        raise NotFound("Room not available")
+    try:
+        d_start = (
+            date.fromisoformat(start) if start else datetime.now(timezone.utc).date()
+        )
+        d_end = (
+            date.fromisoformat(end)
+            if end
+            else d_start + timedelta(days=DEFAULT_CALENDAR_DAYS)
+        )
+    except ValueError as exc:
+        raise ValueError("Dates must be YYYY-MM-DD") from exc
+    if d_end <= d_start:
+        raise ValueError("end must be after start")
+    if (d_end - d_start).days > MAX_CALENDAR_DAYS:
+        raise ValueError(f"Window may span at most {MAX_CALENDAR_DAYS} days")
+    spans = await crud.get_occupied_ranges(
+        room_id, d_start.isoformat(), d_end.isoformat()
+    )
+    return UnavailableRanges(
+        room_id=room_id,
+        start=d_start.isoformat(),
+        end=d_end.isoformat(),
+        ranges=[DateRange(start=s, end=e) for s, e in spans],
+    )
+
+
 async def get_availability(
     room_id: str, check_in: str, check_out: str
 ) -> AvailabilityResult: