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/Infrastructure/AirGap/IEvidenceSnapshotRepository.cs

@@ -0,0 +1,45 @@
+namespace StellaOps.Findings.Ledger.Infrastructure.AirGap;
+
+/// <summary>
+/// Repository for managing evidence snapshot links.
+/// </summary>
+public interface IEvidenceSnapshotRepository
+{
+    /// <summary>
+    /// Inserts a new evidence snapshot record.
+    /// </summary>
+    Task InsertAsync(EvidenceSnapshotRecord record, CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Gets evidence snapshots for a finding.
+    /// </summary>
+    Task<IReadOnlyList<EvidenceSnapshotRecord>> GetByFindingIdAsync(
+        string tenantId,
+        string findingId,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Gets the latest evidence snapshot for a finding.
+    /// </summary>
+    Task<EvidenceSnapshotRecord?> GetLatestByFindingIdAsync(
+        string tenantId,
+        string findingId,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Gets all evidence snapshots for a bundle.
+    /// </summary>
+    Task<IReadOnlyList<EvidenceSnapshotRecord>> GetByBundleUriAsync(
+        string tenantId,
+        string bundleUri,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Checks if an evidence snapshot exists and is not expired.
+    /// </summary>
+    Task<bool> ExistsValidAsync(
+        string tenantId,
+        string findingId,
+        string dsseDigest,
+        CancellationToken cancellationToken);
+}