Register all adapters in AdapterRegistry

Implement as a Deno TypeScript module (adapter_registry.ts) that can be imported by any Edge Function. Use a Map keyed by `${integrationType}:${orgId}` for the instance cache. The factory pattern should use a static registration map: `const ADAPTER_CONSTRUCTORS: Record = { xledger: XledgerAdapter, dynamics: DynamicsAdapter, ... }` — this makes adding future adapters a one-line change.

For lifecycle management, since Edge Functions are stateless (invocation-scoped), the 'cache' only persists for the duration of one function invocation — document this clearly. The healthCheckAll() method should use Promise.allSettled() (not Promise.all()) to ensure one failing health check does not block results from others. The availability check should query the integration_configurations table (via the repository layer from task-002) to verify an active config exists for the org + type combination before attempting instantiation. This prevents wasteful adapter construction when no config is set up.

Graceful degradation: wrap each healthCheck() call in try/catch and return a HealthResult with status: 'unavailable' and the error message on failure — never propagate raw exceptions from health checks.

Unit tests (Deno test): getAdapter returns correct adapter class for each of the five integration types, AdapterNotFoundError thrown for unknown type, org isolation verified (same type different org returns different instance with different credentials), isAdapterAvailable returns false when no config exists, healthCheckAll() resolves concurrently and maps all five results correctly, graceful degradation when one healthCheck throws (others still resolve). Mock all five adapter constructors and credential vault to keep tests fast and dependency-free. Test coverage target: 95% on registry logic. Run in CI on every commit since this is a critical routing layer.