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>

tests/pg/parties-phase0.pg.test.ts

@@ -0,0 +1,36 @@
+import { describe, expect, it } from 'vitest'
+import { getPool } from './setup'
+
+/**
+ * Parties, phase 0 (migration 20260902120000): pg_trgm is available for
+ * trigram blocking of counterparty keys, and the two context-graph tables
+ * whose feature code was never merged are gone, so local replays agree with
+ * prod (where they were dropped during the context-graph revert).
+ */
+describe('parties phase 0 (pg)', () => {
+  it('pg_trgm is installed', async () => {
+    const { rows } = await getPool().query<{ n: number }>(
+      `SELECT count(*)::int AS n FROM pg_extension WHERE extname = 'pg_trgm'`,
+    )
+    expect(rows[0]!.n).toBe(1)
+  })
+
+  it('trigram similarity ranks the same vendor above a different one', async () => {
+    const { rows } = await getPool().query<{ same: number; other: number }>(
+      `SELECT extensions.similarity('levfakt beijer byggmaterial 097', 'beijer byggmaterial') AS same,
+              extensions.similarity('levfakt beijer byggmaterial 097', 'skelleftea plat') AS other`,
+    )
+    expect(Number(rows[0]!.same)).toBeGreaterThan(Number(rows[0]!.other))
+    expect(Number(rows[0]!.same)).toBeGreaterThan(0.3)
+  })
+
+  it('the reverted context-graph tables are gone', async () => {
+    const { rows } = await getPool().query<{ n: number }>(
+      `SELECT count(*)::int AS n
+       FROM pg_tables
+       WHERE schemaname = 'public'
+         AND tablename IN ('graph_counterparties', 'graph_transaction_counterparties')`,
+    )
+    expect(rows[0]!.n).toBe(0)
+  })
+})