fix(hotel_receptionist): stop book_room offering views a room type doesn't have

[u9g]

Ports the book_room.py changes out of #6567 so they can land on their own.

Summary

• set_stay's options became one line per room type, each carrying its own view verdict. The single pipe-delimited line (queen 2beds (city or garden views) | ... | double queen (ocean view)) read as one blob, so the model bound a neighboring type's view to the type the caller picked and offered a garden-view double queen — a room that has never existed. The line also says whether the view is a question (two available) or a fact (one), which stops the offer from becoming a false choice.
• Weekday names in set_stay and in the read-back directive are now computed from the dates instead of left to model day-counting, where a hallucinated weekday survives every read-back.
• confirm_booking's missing-field guard raised _status(), which reads as "here is the next step" and says nothing about whether a reservation exists. By that point in a multi-room call the model has usually already spoken a real HTL- code, so it invented one and told the caller they were booked. The refusal path now names the outcome; is_error can't carry it, since the OpenAI provider format drops the flag and sends a tool message whose content is that string and nothing else.
• Instructions state the flow holds exactly one room: set_stay / choose_room replace values rather than adding a second room, so a caller wanting two rooms gets one flow each.

The option formatting moves to hotel_db.describe_room_options in a pure-move commit first, then changes shape.

tools_rooms.py's read-only availability tool still renders views in the old form and is left alone here.

Testing

• uv run pytest --unit (1942 passed, 5 skipped — unchanged from main)
• make lint / make format-check
• Smoke-ran set_stay, _status(), _not_booked(), and describe_room_options against the seeded DB; verified the pure-move commit renders a string identical to the old inline expression

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.