feat: upgrade JetStreamService to lifecycle orchestrator

Implements enableJetStream() semantics from golang/nats-server/server/jetstream.go:414-523.

- JetStreamService.StartAsync(): validates config, creates store directory
  (including nested paths via Directory.CreateDirectory), registers all
  $JS.API.> subjects, logs startup stats; idempotent on double-start
- JetStreamService.DisposeAsync(): clears registered subjects, marks not running
- New properties: RegisteredApiSubjects, MaxStreams, MaxConsumers, MaxMemory, MaxStore
- JetStreamOptions: adds MaxStreams and MaxConsumers limits (0 = unlimited)
- FileStoreConfig: removes duplicate StoreCipher/StoreCompression enum declarations
  now that AeadEncryptor.cs owns them; updates defaults to NoCipher/NoCompression
- FileStoreOptions/FileStore: align enum member names with AeadEncryptor.cs
  (NoCipher, NoCompression, S2Compression) to fix cross-task naming conflict
- 13 new tests in JetStreamServiceOrchestrationTests covering all lifecycle paths

src/NATS.Server/JetStream/Storage/FileStoreOptions.cs

@@ -6,8 +6,20 @@ public sealed class FileStoreOptions
     public int BlockSizeBytes { get; set; } = 64 * 1024;
     public string IndexManifestFileName { get; set; } = "index.manifest.json";
     public int MaxAgeMs { get; set; }
+
+    // Legacy boolean compression / encryption flags (FSV1 envelope format).
+    // When set and the corresponding enum is left at its default (NoCompression /
+    // NoCipher), the legacy Deflate / XOR path is used for backward compatibility.
     public bool EnableCompression { get; set; }
     public bool EnableEncryption { get; set; }
+
     public bool EnablePayloadIntegrityChecks { get; set; } = true;
     public byte[]? EncryptionKey { get; set; }
+
+    // Go parity: StoreCompression / StoreCipher (filestore.go ~line 91-92).
+    // When Compression == S2Compression the S2/Snappy codec is used (FSV2 envelope).
+    // When Cipher != NoCipher an AEAD cipher is used instead of the legacy XOR.
+    // Enums are defined in AeadEncryptor.cs.
+    public StoreCompression Compression { get; set; } = StoreCompression.NoCompression;
+    public StoreCipher Cipher { get; set; } = StoreCipher.NoCipher;
 }