Add property-based tests for SBOM/VEX document ordering and Unicode normalization determinism

- Implement `SbomVexOrderingDeterminismProperties` for testing component list and vulnerability metadata hash consistency.
- Create `UnicodeNormalizationDeterminismProperties` to validate NFC normalization and Unicode string handling.
- Add project file for `StellaOps.Testing.Determinism.Properties` with necessary dependencies.
- Introduce CI/CD template validation tests including YAML syntax checks and documentation content verification.
- Create validation script for CI/CD templates ensuring all required files and structures are present.

src/Concelier/StellaOps.Concelier.WebService/Options/ConcelierOptions.cs

@@ -44,6 +44,12 @@ public sealed class ConcelierOptions
     /// </summary>
     public FederationOptions Federation { get; set; } = new();
 
+    /// <summary>
+    /// Feed snapshot configuration for atomic multi-source snapshots.
+    /// Per DET-GAP-03 in SPRINT_20251226_007_BE_determinism_gaps.
+    /// </summary>
+    public FeedSnapshotOptions FeedSnapshot { get; set; } = new();
+
     /// <summary>
     /// Stella Router integration configuration (disabled by default).
     /// When enabled, ASP.NET endpoints are automatically registered with the Router.
@@ -303,4 +309,41 @@ public sealed class ConcelierOptions
         /// </summary>
         public bool RequireSignature { get; set; } = true;
     }
+
+    /// <summary>
+    /// Feed snapshot options for atomic multi-source snapshots.
+    /// Per DET-GAP-03 in SPRINT_20251226_007_BE_determinism_gaps.
+    /// </summary>
+    public sealed class FeedSnapshotOptions
+    {
+        /// <summary>
+        /// Enable feed snapshot endpoints.
+        /// </summary>
+        public bool Enabled { get; set; }
+
+        /// <summary>
+        /// Maximum list page size for snapshot listing.
+        /// </summary>
+        public int MaxListPageSize { get; set; } = 100;
+
+        /// <summary>
+        /// Maximum bundle size in bytes for import (default 1GB).
+        /// </summary>
+        public long MaxBundleSizeBytes { get; set; } = 1024L * 1024 * 1024;
+
+        /// <summary>
+        /// Snapshot retention days. Snapshots older than this are automatically cleaned up.
+        /// </summary>
+        public int RetentionDays { get; set; } = 90;
+
+        /// <summary>
+        /// Path to store snapshot bundles.
+        /// </summary>
+        public string StoragePath { get; set; } = System.IO.Path.Combine("out", "snapshots");
+
+        /// <summary>
+        /// Default compression algorithm for exports.
+        /// </summary>
+        public string DefaultCompression { get; set; } = "zstd";
+    }
 }