Replace rich SPM provenance with compact typed receipts

[anth-volk]

Fixes #715

Summary

• replaces rich country-owned SPM diagnostics on the public wire with strict compact individual and comparison receipts
• makes compact spm_provenance the sole source of completed-result forecast, scenario, geography, county-vintage, and date configuration
• removes the sibling spm_config object from direct, segmented-national, budget-window, generated-client, and temporary Stage 12 completed-result contracts
• stores only the compact receipt in Stage 12 calculation artifacts and derives internal resolved configuration from that receipt
• rejects the former dual-field completed-result and Stage 12 artifact shapes rather than accepting them as compatibility inputs
• regenerates and verifies the gateway and Cloud Run OpenAPI contracts and generated Python client

Validation

• shared contract and gateway-model suites: 105 passed
• direct, segmented-national, budget-window, output-builder, and Stage 12 focused suites: 209 passed, 3 skipped
• gateway SPM routes and OpenAPI golden: 91 passed
• Cloud Run entry OpenAPI suite: 4 passed
• generated-client SPM suite: 6 passed
• focused Pyright: 0 errors
• Ruff formatting and checks passed on changed files

Individual compact receipts remain below 1 KiB and a 20-segment comparison remains below 2 KiB. Calculation code and numerical result assembly are unchanged.