refactor(cam): rename read-noise path to read-pass-through and reorganize test module structure

- Rename `read_noise` scenarios and noise_mode to `read_pass_through` across
  run_cam_correctness.py, test_run_cam_correctness.py, and Makefiles
- Update RTL comment in match_engine_pipeline.sv to reflect pass-through behavior
- Move unit-level cocotb tests from `tests.test_*` flat namespace to
  `tests.modules.*` and `tests.top.*` subdirectory layout, matching actual
  Makefile paths (hw/sim/tests/modules/..., hw/sim/tests/top/...)
- Remove redundant dual-noise subtarget from read_noise/Makefile
- Update help text and docs to reflect read-path pass-through semantics
- Add .codegraph to .gitignore

hw/sim/Makefile

@@ -7,11 +7,11 @@ TOP_CONFIGS := no_noise write_noise read_noise
 help:
 	@echo "Available hw/sim targets:"
 	@echo "  make test-model"
-	@echo "  make test-top             # 默认运行所有顶层噪声配置"
-	@echo "  make test-top-all         # 运行所有顶层噪声配置"
+	@echo "  make test-top             # 默认运行所有顶层配置"
+	@echo "  make test-top-all         # 运行所有顶层配置"
 	@echo "  make test-top-no_noise    # 无噪声集成测试"
 	@echo "  make test-top-write_noise # 写入噪声集成测试"
-	@echo "  make test-top-read_noise  # 读取噪声集成测试"
+	@echo "  make test-top-read_noise  # 读取路径 pass-through 集成测试"
 	@echo "  make test-module MODULE=cam_core_banked"
 	@echo "  make test-modules"
 	@echo "  make test-perf"

hw/sim/tests/modules/cam_read_noise/test_cam_read_noise.py

@@ -52,7 +52,7 @@ async def read_noise_disabled_forwards_hashes_after_one_stage(dut):
 
 @cocotb.test()
 async def read_noise_enabled_still_forwards_hashes_unmodified(dut):
-    """With READ_NOISE_EN=1, the pass-through still forwards hashes unmodified."""
+    """The read path pass-through forwards hashes unmodified."""
     cocotb.start_soon(Clock(dut.clk, 10, unit="ns").start())
     await reset_read_noise(dut)
 

hw/sim/tests/top/read_noise/Makefile

@@ -6,17 +6,10 @@ TOPLEVEL := cam_top
 COCOTB_TEST_MODULES := tests.top.read_noise.test_read_noise
 VERILOG_SOURCES := $(RTL_CAM_TOP)
 
-# 读取噪声开启（Phase 2 后为 pass-through），写入噪声默认关闭
+# 读取路径 pass-through 配置，写入噪声默认关闭
 WRITE_NOISE_EN := 0
 
 include $(SIM_ROOT)/mk/cocotb-common.mk
 
-# ── 写入+读取双重噪声子目标 ─────────────────────────────────────────
-.PHONY: test-with-write-noise
-
-test-with-write-noise:
-	$(MAKE) -B -f Makefile results.xml WRITE_NOISE_EN=1 \
-	  COCOTB_TEST_FILTER=read_noise_model_match
-
 clean::
 	rm -rf sim_build