fix: shared_experts gate_up_proj stacking was skipped by .experts. check

The stacking logic skipped any key containing '.experts.' to avoid
MoE routed expert weights. But 'shared_experts' also matches that
substring, so gate_proj and up_proj were never stacked into
gate_up_proj. Changed to '.ffn.experts.' which only matches the
routed experts path.

Also includes POST-LOAD all-zero param scan.

vllm/patches/deepseek_v4.py

@@ -1311,8 +1311,10 @@ class DeepseekV4Model(nn.Module):
                     break  # first match wins (order matters)
 
             for param_name, weight_name, shard_id in stacked_params_mapping:
-                # Skip non-stacked layers and experts (experts handled below).
-                if ".experts." in name:
+                # Skip MoE routed experts (handled separately below).
+                # Use .ffn.experts. (not .experts.) to avoid skipping
+                # shared_experts which also contains ".experts.".
+                if ".ffn.experts." in name:
                     continue
                 if weight_name not in name:
                     continue
@@ -1370,7 +1372,7 @@ class DeepseekV4Model(nn.Module):
                 loaded_params.add(name)
                 break
             else:
-                if ".experts." in name:
+                if ".ffn.experts." in name:
                     # E8M0 scales are stored as float8_e8m0fnu in
                     # MXFP4 checkpoints but NVFP4 uses float8_e4m3fn.
                     # The uint8 view+copy path is only valid for MXFP4;