Add regions support for geographic analysis

[anth-volk]

Summary

Add support for regions (geographic areas) in the API to enable location-specific policy analysis.

Requirements

• Create Region database model with fields:

  • code - Region identifier (e.g., "state/ca", "us")
  • label - Display name (e.g., "California")
  • region_type - Type of region (e.g., "state", "congressional_district")
  • requires_filter - Whether dataset filtering is needed
  • filter_field / filter_value - Parameters for dataset filtering
  • dataset_id - Associated dataset
  • tax_benefit_model_id - Associated model

• Create REST endpoints:

  • GET /regions/ - List regions with optional filters
  • GET /regions/{region_id} - Get region by ID
  • GET /regions/by-code/{region_code} - Get region by code

• Add seed data for US and UK regions

• Integrate with analysis endpoint to support region-level simulations

Related

• policyengine.py PR chore(deps): update policyengine-us to 1.634.8 #231 adds dataset filtering support
• App v2 branch feat/migrate-geographies-to-v2 adds frontend regions hook