Add fulldata MAM DAPT encoder (revision 2.2)

SHA-256: 0fe9f7dd92780c2e564f1df06a192482dbcb9a56bdab4202f4d94862b9168f89
Training: MAM with k=1024 k-means tokeniser on 5,673-h World-DAPT corpus, 126,365 steps, batch 16, lr 1e-4 cosine, bfloat16. Replaces buggy SimCLR/AMP-fp16 weights (legacy beats_dapt_topup_encoder.pt = PRETRAIN-equivalent).

beats_dapt_mam_step120000.pt

@@ -0,0 +1,3 @@
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+size 361343579