Support the FHIR PATCH interaction (FHIRPath Patch)

[schwzr]

Closes #552

Summary

Adds support for the FHIR PATCH interaction using the FHIRPath Patch format (a Parameters resource, https://www.hl7.org/fhir/R4/fhirpatch.html):

• Direct REST: PATCH [type]/[id] and conditional PATCH [type]?[criteria]
• Inside transaction and batch bundles (Bundle.entry.request.method = PATCH)
• Advertised as a supported interaction in the CapabilityStatement

A patch is applied to a copy of the current resource and then written through the existing update code path, so authorization (reasonUpdateAllowed(old, patched)), validation, optimistic locking (If-Match), versioning and the Prefer header behave exactly as for an update. PATCH maps to the existing UPDATE role — no new permission is required.

Implementation

• FhirPathPatchService — new engine applying add / insert / delete / replace / move on the HAPI R4 runtime model (FhirContext / IFhirPath). No new runtime dependency — deliberately avoids hapi-fhir-storage (which would pull in hapi-fhir-server, JPA/Hibernate, Quartz, Spring-tx).
• REST: new @PATCH JAX-RS annotation (JAX-RS ships none), patch(...) on BasicResourceService and the abstract jaxrs / secure / impl layers. The patch service is provided through the already-injected ParameterConverter singleton to avoid threading a new constructor argument through all ~28 resource services.
• Bundle: new PatchCommand (resolves the target DAO from the request URL like DeleteCommand, transaction priority 3 like update) plus a PATCH branch in CommandFactoryImpl and the audit log.
• Client: FhirWebserviceClient.patch(...) / patchConditionaly(...).

Scope

In scope: FHIRPath Patch (add / insert / delete / replace / move), REST (standard + conditional), transaction + batch bundles, client support, tests.

Out of scope (for now):

• JSON Patch (application/json-patch+json) and XML Patch — omitted to keep the dependency footprint minimal; FHIRPath Patch is also the format FHIR recommends for FHIR resources. Can be added later.
• Resolving temporary (urn:uuid:) references contained inside patch values when processed within a bundle.

Testing

• Unit tests — FhirPathPatchServiceImplTest: 12/12 (all five operation types incl. list mutation and error handling).
• Integration tests — PatchIntegrationTest: 5/5 (REST, conditional, transaction bundle, 404 not-found, 400 bad-request) against a real server + PostgreSQL (Testcontainers).
• Regression — full server unit suite 231/231 green; full FHIR integration suite 496/497 green. The single failure is the pre-existing flaky ParallelCreateIntegrationTest#testCreateDuplicateStructureDefinitionsParallelDirect (a parallel race test): it passes on develop and passes/fails intermittently on this branch (~50%), and this change touches no create / DAO / unique-constraint code.

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