FilteringMetadataCache is a monolithic class that handles collection metadata recovery, database metadata recovery, lifecycle management, and shared utilities all in a single flat interface.

This ticket decomposes the class into a facade pattern:

• ShardMetadataRecoveryHandler becomes the facade. It owns the CatalogCache and ShardServerCatalogCacheLoader, remains registered as a ServiceContext decoration, and handles lifecycle operations. It delegates recovery work to two domain-specific handlers.
• ShardCollectionMetadataRecoveryHandler handles collection version mismatch recovery (onShardVersionMismatch), collection flush, end-marker notifications, and forced collection refresh. It internally dispatches between authoritative and non-authoritative code paths based on feature flags.
• ShardDatabaseMetadataRecoveryHandler handles database version mismatch recovery (onDbVersionMismatch), database flush, and forced database refresh, with the same authoritative/non-authoritative dispatch.

This is a pure structural refactor with no behavioral changes.