feat(sha3_chain): add simple SHA3_G integration test

Phase 3.2: Verifies module chaining works.
- sha3_chain_top.v: 3-state FSM (IDLE→BUSY→DONE), feeds d_in→sha3_top(G)
- Captures rho[255:0] and sigma[511:256] from SHA3-512 output
- Verified: 3/3 bit-exact vs Python G(d||k=2) reference

KG full-path FSM (~11 module chain) deferred — too complex for single dispatch.

test_framework/modules/sha3_chain/test_plan.json

@@ -0,0 +1,14 @@
+{
+  "module": "sha3_chain",
+  "rtl_top": "sync_rtl/sha3_chain/sha3_chain_top.v",
+  "rtl_deps": ["sync_rtl/sha3/keccak_round.v", "sync_rtl/sha3/keccak_core.v", "sync_rtl/sha3/sha3_top.v"],
+  "tb_cpp": "sync_rtl/sha3_chain/TB/tb_sha3_chain.cpp",
+  "timeout_s": 60,
+  "cases": [{
+    "id": "basic",
+    "description": "d → SHA3_G(d||k=2) → rho, sigma vs Python G()",
+    "params": {"k": 2},
+    "num_vectors": 3,
+    "tolerance": "bit_exact"
+  }]
+}