[EPAC-2153]: add MP lobbying exposure endpoint

[riddim-developer-bot]

Summary

• Adds the LoadMPLobbyingExposure use case, domain models, Postgres repository, precompute read models, and Lambda route for GET /api/v1/members/{id}/lobbying-exposure.
• Adds MP lobbying timeline, summary, and subject-breakdown migration tables with OpenAPI, deployment manifest, and architecture catalog updates.
• Adds coverage for populated/empty MPs, 50-row pagination, window filters, handler parsing, and repository refresh/load behavior.

Verification

• go test ./... (backend/lobbying)
• go test ./... (backend/openapi)
• scripts/ci/check_go_dependency_rule.sh
• scripts/ci/check_catalog_drift.sh
• jq empty backend/manifest/deployment-services.json
• jq empty backend/openapi/openapi.json
• go test -tags=integration ./... (backend/lobbying)
• go test -tags=integration -run TestPostgresMPLobbyingRepositoryRefreshesAndLoadsExposure -v ./repository (skipped locally: DATABASE_URL not set; CI should exercise it when a database is configured)

Acceptance Criteria

• MPLobbyingSummary aggregate precomputed per MP per quarter/window with total communications, unique organizations, most frequent subject, top 3 organizations, and previous-Parliament trend.
• GET /members/{member_id}/lobbying-exposure and /api/v1/members/{id}/lobbying-exposure return summary plus 50-row paged timeline.
• Timeline rows include date, organization + sector, subject matter, communication type, high-confidence bill cross-reference only, OCL citation, and source URL.
• Subject breakdown returns all subject counts for charting.
• Party and national averages are computed from the current-Parliament cohort during quarterly summary refresh.
• Empty MPs return HTTP 200-compatible empty arrays and zero-count summary.
• Human Handoff issue includes: Spot-check 5 MPs' Lobbying exposure endpoint against OCL for accuracy.

Release-Note: Adds the MP lobbying exposure API endpoint backed by precomputed OCL summaries.