Backfill recorded weather for every night in the hotel's history #91

Blocked by: #83

Problem

The model learns from past nights, so it needs the weather that actually happened on each of them. The weather backfill exists, but nothing makes sure it covers the full range of the hotel's history, and gaps silently weaken training.

Goal

Every night in the hotel's history has recorded weather, and any gap is known.

Scope

• Run the weather backfill for each hotel over the full range of its PMS history (two years once the Guestline exports are in).
• Use the weather coverage endpoint to find and fill gaps.
• Write down any days the source can't provide.

Considerations

• Recorded weather replaces forecasts for past days; check that no past night is left with only a forecast.
• Re-run the gap check after each large history upload.

Acceptance criteria

• The coverage check reports no gaps over the hotel's history, or each remaining gap is explained.
• No past night uses forecast weather when recorded weather exists.