feat: Implement air-gap functionality with timeline impact and evidence snapshot services

- Added AirgapTimelineImpact, AirgapTimelineImpactInput, and AirgapTimelineImpactResult records for managing air-gap bundle import impacts.
- Introduced EvidenceSnapshotRecord, EvidenceSnapshotLinkInput, and EvidenceSnapshotLinkResult records for linking findings to evidence snapshots.
- Created IEvidenceSnapshotRepository interface for managing evidence snapshot records.
- Developed StalenessValidationService to validate staleness and enforce freshness thresholds.
- Implemented AirgapTimelineService for emitting timeline events related to bundle imports.
- Added EvidenceSnapshotService for linking findings to evidence snapshots and verifying their validity.
- Introduced AirGapOptions for configuring air-gap staleness enforcement and thresholds.
- Added minimal jsPDF stub for offline/testing builds in the web application.
- Created TypeScript definitions for jsPDF to enhance type safety in the web application.

src/Findings/StellaOps.Findings.Ledger/Domain/LedgerEventConstants.cs

@@ -15,6 +15,8 @@ public static class LedgerEventConstants
     public const string EventFindingAttachmentAdded = "finding.attachment_added";
     public const string EventFindingClosed = "finding.closed";
     public const string EventAirgapBundleImported = "airgap.bundle_imported";
+    public const string EventEvidenceSnapshotLinked = "airgap.evidence_snapshot_linked";
+    public const string EventAirgapTimelineImpact = "airgap.timeline_impact";
     public const string EventOrchestratorExportRecorded = "orchestrator.export_recorded";
 
     public static readonly ImmutableHashSet<string> SupportedEventTypes = ImmutableHashSet.Create(StringComparer.Ordinal,
@@ -29,6 +31,8 @@ public static class LedgerEventConstants
         EventFindingAttachmentAdded,
         EventFindingClosed,
         EventAirgapBundleImported,
+        EventEvidenceSnapshotLinked,
+        EventAirgapTimelineImpact,
         EventOrchestratorExportRecorded);
 
     public static readonly ImmutableHashSet<string> FindingEventTypes = ImmutableHashSet.Create(StringComparer.Ordinal,