Use AES for initialized 128-bit Rijndael using resources

Port closed parenthesized RijndaelManaged using resources whose initializer establishes literal BlockSize 128 before IV. Keep remaining setters in order before the disposal boundary, retain FeedbackSize 128 and allow bound block-size reads. Reject later geometry writes, escapes, cleanup, captures and conditional snapshots. Existing plain/scoped recipes retain their bounds; no algorithm or key choice.