fix stale IMAP connection: clean up old connection on reconnect, robust disconnect

- connect() now cleans up any stale connection/event loop group before
  creating a new one, preventing leaked resources after failed syncs
- disconnect() uses try? for both channel close and group shutdown so
  "Already closed" errors don't prevent cleanup

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Packages/MagnumOpusCore/Sources/IMAPClient/IMAPClient.swift

@@ -20,6 +20,14 @@ public actor IMAPClient: IMAPClientProtocol {
 	// MARK: - Connection lifecycle
 
 	public func connect() async throws {
+		// Clean up any stale connection from a previous failed sync
+		if connection != nil {
+			try? await connection?.disconnect()
+			try? await connection?.shutdown()
+			connection = nil
+			runner = nil
+		}
+
 		let conn = IMAPConnection(host: host, port: port)
 		try await conn.connect()
 		connection = conn
@@ -36,8 +44,8 @@ public actor IMAPClient: IMAPClientProtocol {
 			_ = try? await r.run(.logout)
 			runner = r
 		}
-		try await connection?.disconnect()
-		try await connection?.shutdown()
+		try? await connection?.disconnect()
+		try? await connection?.shutdown()
 		connection = nil
 		runner = nil
 	}