chore(env-doc): allowlist VT_MLA_FUSED_NORM_ROPE (A5 fold rollback flag)

The MLA A2+A5 fold (c1ffa311) added the VT_MLA_FUSED_NORM_ROPE A/B rollback
switch for the shared kFusedNormRope op but did not allowlist it — check-env-doc
went RED on main. It is a kernel-internal tuning switch (sibling of the other
VT_MLA/VT_V4 fold flags), so it belongs on the allowlist. Fix-forward.

FOLLOWING_AGENTS_PROTOCOL
Assisted-by: Claude Code:claude-opus-4-8 [ClaudeCode]

Author: mudler

scripts/env-doc-allowlist.txt

@@ -152,3 +152,4 @@ VT_V4_Q8_PAIR
 VT_V4_Q8_PROBE
 VT_V4_Q8_ILP
 VT_V4_Q8_PREFETCH
+VT_MLA_FUSED_NORM_ROPE