enhancement: implement FHIRPath-filtered obligation evaluation

[Ardenexal]

Component

Validation

FHIR Version

R4, R4B, R5 (all versions)

Problem Statement

FHIRValidationService::collectObligationViolations() silently skips all #[FHIRObligation] instances where $obligation->filter !== null. Conditional obligations (e.g. "populate this field only if another field has value X") are never evaluated.

if ($obligation->filter !== null) {
    continue; // FHIRPath filter evaluation deferred to backlog
}

Proposed Solution

Use the existing FHIRPathService to evaluate $obligation->filter against the resource instance. Only apply the obligation if the filter evaluates to true. If evaluation throws, emit a distinct INFO violation ("filter indeterminate") matching the approach proposed for invariant eval errors.

Additional Context

The FHIRObligation attribute already carries the filter property; only the runtime evaluation step is missing.