PyGeoAPI matview refresh should run from app layer instead of pg_cron

[kbighorse]

Currently the nightly refresh of PyGeoAPI materialized views is scheduled with pg_cron in the database. The same refresh can be run from the app layer via the existing CLI:

uv run python -m cli.cli refresh-pygeoapi-materialized-views

Requested action: If we prefer not to rely on pg_cron (e.g. to simplify DB requirements or support managed Postgres that doesn't offer pg_cron), we can:

1. Remove pg_cron scheduling from the migration (and from Docker/CI).
2. Schedule the CLI command via system cron, Render Cron, or another scheduler that runs e.g. daily at 03:00.

No change to the materialized views themselves; only who triggers the refresh. Document the chosen schedule (e.g. in README or runbook).