Feat/payment state durability

[1amKhush]

Closes #109

Summary

Harden CEP-8 server payments against duplicate billing, stale verifier completions, and state loss across workers or restarts.

• Add atomic admission, generation-fenced transitions, and single-use authorization claims.
• Retain invoice bindings and replay records independently of verification expiry.
• Support an injectable PostgreSQL backend alongside the in-memory default.
• Validate quotes, amount units, processor output, and PMI compatibility.
• Add canonical identity fixtures and PostgreSQL integration coverage in CI.

Compatibility

• AuthorizationStore now uses async admit, transition, and read.
• PostgreSQL is available through @contextvm/sdk/payments/postgres; call initialize() before injecting the store.
• Invalid configuration, out-of-range quotes, and disjoint PMI sets are rejected.

Validation

• 784 tests passed; 5 live-wallet tests skipped.
• Covered concurrent workers, worker crash/restart, stale attempts, lost commit acknowledgements, and encrypted replay.
• Typecheck, lint, build, export checks, and frozen lockfile validation passed.
• Node 18 public API/lifecycle smoke tests and browser bundle checks passed.

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