Implement Advisory Canonicalization and Backfill Migration

- Added AdvisoryCanonicalizer for canonicalizing advisory identifiers.
- Created EnsureAdvisoryCanonicalKeyBackfillMigration to populate advisory_key and links in advisory_raw documents.
- Introduced FileSurfaceManifestStore for managing surface manifests with file system backing.
- Developed ISurfaceManifestReader and ISurfaceManifestWriter interfaces for reading and writing manifests.
- Implemented SurfaceManifestPathBuilder for constructing paths and URIs for surface manifests.
- Added tests for FileSurfaceManifestStore to ensure correct functionality and deterministic behavior.
- Updated documentation for new features and migration steps.

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

@@ -144,7 +144,7 @@ public sealed class ConcelierOptions
 
     public sealed class FeaturesOptions
     {
-        public bool NoMergeEnabled { get; set; }
+        public bool NoMergeEnabled { get; set; } = true;
 
         public bool LnmShadowWrites { get; set; } = true;