feat(parties): phase 0 prerequisites, pg_trgm and golden-set draw (#2157)

* feat(parties): phase 0 prerequisites, pg_trgm and golden-set draw

Phase 0 of the Kontakter plan: make the counterparty resolver measurable
before building it.

- Migration 20260902120000 enables pg_trgm (trigram blocking of
  counterparty keys) and drops the two context-graph tables from
  20260706193007 whose feature code was never merged and which prod no
  longer has, so fresh replays agree with prod.
- tests/pg/parties-phase0.pg.test.ts pins the extension, a sanity check on
  trigram ranking, and the absence of the graph tables.
- scripts/parties/draw-golden-set.sql is the reproducible, read-only draw
  of the 200-key labelling sample (three strata, md5-ordered) and the
  payee-identity base rate. The drawn rows contain customer voucher text
  and are kept in gitignored dev_docs, never in this public repo.
- scripts/parties/README.md records the label vocabulary and the numbers
  measured on prod on 2026-09-02.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* fix(archive): drop the two context-graph tables from the archive contract

The migration in this PR removes graph_counterparties and
graph_transaction_counterparties, so the full-archive contract must stop
classifying them: tests/schema/no-phantom-columns.test.ts asserts that
every classified table exists in the migration replay, and the live-DB
twin in tests/pg/full-archive-coverage.pg.test.ts asserts the same against
information_schema.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

---------

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

lib/reports/full-archive-export.ts

@@ -1197,8 +1197,6 @@ export const ARCHIVE_EXCLUDED_TABLES: Record<string, string> = {
     'WORM verification log (SHA-256 recompute outcomes); failures reach the archive via audit_log in revision/behandlingshistorik.json',
   event_log: '30-day TTL event bus log',
   extension_data: 'extension runtime state (includes this backup\'s own state)',
-  graph_counterparties: 'derived AI context graph, regenerable',
-  graph_transaction_counterparties: 'derived AI context graph, regenerable',
   idempotency_keys: 'infrastructure',
   inbox_rate_counters: 'infrastructure',
   mail_connections: