/reports takes data_source: "local_area_dataset" for UK-wide and nation reports, and no request takes dataset_name #1069

UK-wide and nation reports in the detailed-save path need their constituency and local-authority results. #1068 makes the v2 coordinator and UK workers calculate them for a report on the bundle's local-area dataset (microcosm_uk_2024_25_dense on PolicyEngine.py 6.17.1), but no request can ask for that dataset: POST /reports takes a dataset_name that names any catalog dataset, and nothing else.

Wanted:

• POST /reports economy reports take data_source: "local_area_dataset": a UK-wide or nation report runs on the dataset the default v2 worker's UK manifest entry declares for local-area reports, and returns its full results with its areas. Any other value, any other country or region, and a release that routes constituencies and local authorities to no dataset of their own are refused with 422.
• No /reports, /simulations or budget-window request takes dataset_name: a report or simulation runs on the dataset the catalog gives its region. The Public API stops sending the key first (Stop sending dataset_name to the simulation service, and refuse it on /v2 policyengine-api#4307).
• The staging economy check's current-law Wales 2026 report runs on the local-area dataset, so each deploy calculates a nation's areas.