feat: consume ledger posting commands

[ramioooz]

Summary

• Consume governed LedgerPostingRequested.v1 commands in Ledger Service.
• Persist an inbox record for durable event-id deduplication and redelivery handling.
• Reuse the existing immutable, balanced, idempotent ledger posting use case.
• Keep the consumer disabled by default until SIT producer/topic configuration is enabled.
• Publish this runtime change as image 0.0.4 with Helm chart 0.4.0.

Project tracking

• Parent task: TASK: Consume ledger posting commands in Ledger Service .github#211
• Parent story: STORY: Orchestrate transfer saga with ledger-driven completion .github#103
• Sprint 3 epic: EPIC: Sprint 3 - Internal Transfers and Event Consistency .github#21

Verification

• ./mvnw --batch-mode --no-transfer-progress verify
• Unit phase: 21 tests passed.
• Integration phase: 28 tests passed, including Testcontainers PostgreSQL.
• helm lint helm --strict --values helm/values-sit.yaml
• helm template ledger-service helm --namespace digital-bank-sit --values helm/values-sit.yaml
• git diff --check

Merge and rollout

This PR can merge after the existing Transaction Service producer and SIT topic/configuration PRs are available. There is no required delay between merges. Enable ledger.posting.consumer.enabled only after the governed topic and producer are deployed, then roll out Ledger Service with image digital-bank-java/ledger-service:0.0.4.

No public HTTP route is added. The consumer maps the governed command into the existing internal ledger posting path, while the inbox and database uniqueness constraints protect redelivery and concurrent processing.

[ramioooz]

Related delivery links:

• Parent task: digital-bank-java/.github#211
• Parent story: digital-bank-java/.github#103
• Transaction producer/process-manager integration: transaction-service#13
• Transaction SIT rollout/configuration: transaction-service#15 and config-repo#38

Merge order: those Transaction Service and SIT configuration changes are already merged. This Ledger consumer PR can merge now; no delay is required. Enable ledger.posting.consumer.enabled only after the governed Kafka topic and producer are deployed, then roll out Ledger Service.

Verification on the branch: ./mvnw --batch-mode --no-transfer-progress verify passed with 21 unit-phase tests and 28 Testcontainers PostgreSQL integration tests; git diff --check passed. The consumer is disabled by default and adds no public HTTP route.

[ramioooz]

Release-safety correction: the consumer branch now publishes image digital-bank-java/ledger-service:0.0.4 and Helm chart 0.4.0 instead of reusing the existing 0.0.3/0.3.0 release. Helm lint, template rendering, and git diff --check pass.