Fix/revenue dashboard

[ahmadalauddin]

What Fixes the 3 reported dashboard issues + the reason none of it worked.

Turned out the DB pool was misconfigured (wrong settings, async-incompatible QueuePool, missing await), so every tenant was just getting hardcoded mock data. Fixed that first, then the actual bugs:

• DB pool use database_url + asyncpg, real data flows now.
• Cache leak key was revenue:{property_id}, no tenant, so tenants with the same property id saw each other's numbers. Namespaced by tenant + added a mismatch guard.
• March totals monthly revenue bucketed in naive UTC, ignored property timezone. 23:30 UTC Feb 29 = Mar 1 in Paris, was counted in Feb. Now derives month bounds in the property's tz in SQL.
• Cent errors money was cast to float. Switched to Decimal.

Tested

docker-compose up --build. Sunset prop-001 → 2250/4, Ocean prop-001 → 0/0, separate cache keys per tenant, March now 2250 not 1000.

Files: database_pool.py, reservations.py, cache.py, dashboard.py