refactor(findings): merge VulnExplorer into Findings Ledger

- Move VulnExplorer DTOs into Ledger WebService Contracts/VulnExplorer/
  (VulnModels, VexDecisionModels, TriageWorkflowModels, AttestationModels,
   FixVerificationModels, EvidenceSubgraphContracts)
- Create VulnExplorerEndpoints.cs mounting all 10 original endpoints
  (/v1/vulns, /v1/vex-decisions, /v1/evidence-subgraph,
   /v1/fix-verifications, /v1/audit-bundles)
- Create adapter services (VulnExplorerAdapters.cs) that delegate to
  existing Ledger services (FindingSummaryService, VulnerabilityDetailService,
  EvidenceGraphBuilder, VexConsensusService)
- Wire VulnExplorer authorization policies and service registrations
  in Ledger Program.cs
- Comment out api (VulnExplorer) container in docker-compose.stella-ops.yml
- Add vulnexplorer.stella-ops.local as network alias on findings-ledger-web
- Update gateway route: /api/vuln-explorer(..) -> findings.stella-ops.local
- Update STELLAOPS_VULNEXPLORER_URL -> findings.stella-ops.local
- Comment out VulnExplorer in services-matrix.env and hosts file
- Update docs: port-registry, component-map, module-matrix, webservice-catalog,
  findings-ledger README
- Eliminates 1 container (stellaops-api)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

devops/compose/hosts.stellaops.local

@@ -19,7 +19,7 @@
 127.1.0.10 excititor.stella-ops.local
 127.1.0.11 vexhub.stella-ops.local
 127.1.0.12 vexlens.stella-ops.local
-127.1.0.13 vulnexplorer.stella-ops.local
+# 127.1.0.13 vulnexplorer.stella-ops.local  # MERGED into findings-ledger-web (SPRINT_20260408_002)
 127.1.0.14 policy-engine.stella-ops.local
 127.1.0.15 policy-gateway.stella-ops.local
 127.1.0.16 riskengine.stella-ops.local