Add ST_H stage: second sha3_top (mb_en=1) computes H(ek) over 800B ek as 6
pre-padded SHA3-256 rate blocks. Per block: assemble 136 bytes (h_padbyte
applies 0x06...0x80 padding on final block) into h_block_r, feed (hold valid
until mb_ready drops), wait permute; capture digest on last block into hek_r.
Full dk readback tap: dk = dk_pke(768) || ek(800) || H(ek)(32) || z(32) = 1632B.
End-to-end TB (tb_mlkem_kg_kat_xsim, no force/release): drive KAT count=0 d/z,
run full KeyGen FSM (IDLE->G->A->C->N->M->E->H->DONE), verify:
ek == KAT pk (800B) byte-exact
dk == KAT sk (1632B) byte-exact
Done in 21403 cycles. ML-KEM-512 KeyGen complete and KAT-verified.
Prior stage TBs (2c/2e/2f) still pass (no regression).
Add ST_N stage: forward NTT (ntt_core mode=0, no scaling) of s[0],s[1],
e[0],e[1] in place (slots S0,S1,E0,E1). Per slot: stream 256 coeffs into
ntt_core during LOAD, collect 256 outputs back to same slot. n_pending
waits for core IDLE between slots.
Verified vs ml-kem-r golden: 1024/1024 shat/ehat coeffs exact (17318 cyc).
RTL was feeding d bytes in reversed order to SHA3-512,
causing G(d) to produce wrong rho/sigma. Fix: add d_rev
wire with byte reversal, connect to sha3_chain_top_shared.