Add household impact analysis endpoints

[anth-volk]

Summary

Extend the Simulation/Report architecture to support household-level impact analysis, allowing users to run household simulations and compare baseline vs reform scenarios.

Dependencies

• Requires Add stored household CRUD support #74 (Stored household CRUD support)

Scope

Model Changes

Simulation model:

• Add SimulationType enum (HOUSEHOLD, ECONOMY)
• Add simulation_type field with default 'economy'
• Make dataset_id nullable (was required)
• Add household_id FK to households
• Add household_result JSONB column for storing calculation output

Report model:

• Add report_type field (household_single, household_comparison, economy_single, economy_comparison)

New Endpoints

• POST /analysis/household-impact - Run household impact analysis
  • If policy_id is None: single run under current law
  • If policy_id is set: comparison (baseline vs reform)
• GET /analysis/household-impact/{report_id} - Get household impact results

Impact Computation

Support all entity types for both countries:

• UK: person, benunit, household
• US: person, tax_unit, spm_unit, family, marital_unit, household

Database

• Migration: 20260203000002_simulation_household_support.sql

Key Features

• Deterministic UUIDs for deduplication/caching
• Reuses existing _calculate_household_uk() and _calculate_household_us() functions
• Stores results in household_result JSONB on Simulation (not Dataset)

Acceptance Criteria

• SimulationType enum and simulation_type field added
• household_id and household_result fields added to Simulation
• report_type field added to Report
• POST endpoint creates correct records (single and comparison)
• GET endpoint returns results with computed impact
• Deduplication working (same params = same IDs)
• Tests passing
• Migration applied successfully