test: install the pg-boss schema the HTTP suite reads

[ethanasm]

Fixes the red Integration job on main (run 31145237749).

What was failing

UnsupportedSchemaError: Schema "pgboss" is empty or not visible to this role.
 ❯ PgBossAdapter.#refs src/pgboss/adapter.ts:76:39
 ❯ PgBossAdapter.queueOverview src/pgboss/adapter.ts:133:18
 ❯ collectSnapshot src/diagnose/engine.ts:51:69
 ❯ test/integration/http-transport.integration.test.ts:170:22

http-transport.integration.test.ts pointed its adapter at a pgboss schema that no suite creates — the version suite installs qd_it_v10/11/12, the graphile suite installs graphile_worker. So it read whatever an earlier run happened to leave in the database: green on a developer's long-lived container, red on CI's fresh one.

Not a flake and not a recent regression — it has failed on every integration run since it landed in abb244a (2026-08-06). The last green CI on main is f5df0a65.

The fix

• The HTTP suite installs pg-boss into its own qd_it_http schema, the way the version suite does with its own.
• The installer moves to a shared test/integration/pgboss-fixture.ts. It drops the schema before installing, so a second local run reads the database it built rather than the one the first run shaped — the same idempotency c672567 gave the graphile suite. The version suite now uses it too (−54 lines of duplicated setup).
• Added expect(snapshot.probe.supported).toBe(true). Every assertion the test had would hold against a schema the transport could not read: the backend name comes from the adapter, findings is an array when the diagnosis is empty, and seen.length > 5 is met by the probe's own queries before anything reads a row. That is why it took a thrown error rather than a failed assertion to surface this.

Verification

Against a real Postgres 16 (postgres:16-alpine, same image CI uses):

• npm run test:integration — 32/32 passed, all 3 files. Run twice back-to-back against the same database to confirm the drop-first fixture is idempotent.
• Confirmed the failure reproduces first without the change (identical UnsupportedSchemaError).
• npm run verify — lint, typecheck, 175 unit tests, build all pass.

No src/ changes; test setup only.

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