[1amKhush]

Add an optional PostgreSQL implementation of PaymentStateStore, separated from #110.

Keep this PR deferred until a deployment needs restart durability or coordination across processes sharing one paying server identity.

Changes

• Add PostgresPaymentStateStore through @contextvm/sdk/payments/postgres.
• Persist invoice bindings, grants, execution records, and replay tombstones.
• Serialize namespace operations using short transactions and generation fences.
• Validate schema versions and consistent worker policies during initialization.
• Propagate database and uncertain commit failures without falling back to memory.
• Add PostgreSQL dependencies, migrations, integration tests, and a PostgreSQL 17.7 CI service.

Applications own the connection pool and must call initialize() before injecting the store.

Validation

• 28 PostgreSQL contract/integration tests and 6 shared PMI regressions passed.
• Covered concurrent workers, worker crashes, reconnects, lost commit acknowledgements, and encrypted replay.
• Typecheck and lint passed.

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