Update hardware-kernels.mermaid.md

Author: t81dev

docs/diagrams/hardware-kernels.mermaid.md

@@ -1,13 +1,17 @@
 ```mermaid
 flowchart TB
-    tryte[Packed trytes (limbs)]
-    load[Load registers (AVX/NEON)]
-    mask[Mask & expand trits]
-    multiply[Multiply columns]
-    accumulate[Accumulate into FP32/BF16]
-    store[Store to output buffer]
-    tryte --> load --> mask --> multiply --> accumulate --> store
-    style load stroke:#333,stroke-width:1px
-    style mask stroke:#f66,stroke-width:1px
-    style multiply stroke:#36c,stroke-width:1px
+  tryte["Packed trytes (limbs)"]
+  load["Load registers (AVX/NEON)"]
+  mask["Mask & expand trits"]
+  multiply["Multiply columns"]
+  accumulate["Accumulate into FP32/BF16"]
+  store["Store to output buffer"]
+
+  tryte --> load --> mask --> multiply --> accumulate --> store
+
+  %% GitHub-friendly styling (avoid hex colors; use named colors)
+  style load stroke:gray,stroke-width:1px
+  style mask stroke:red,stroke-width:1px
+  style multiply stroke:blue,stroke-width:1px
+
 ```