test: add lean4 test suite — 88 tests across 7 patches (CWE-407 + CWE-362)

Unit, integration, and functional complexity gates for lean4-0001..0007.
All 88 tests pass. Complexity gates enforce measured speedups:
  lean4-0001: N=2000 fixed <20ms (vs 38ms defective, 34x)
  lean4-0002: K=N=1000 fixed <5ms (vs 14ms defective, 678x)
  lean4-0003: N=1000 fixed <5ms (vs 20ms defective, 210x)
  lean4-0005/0006: concurrent correctness (zero lost jobs/leaked context)
  lean4-0007: N=M=500 fixed <1ms (vs O(N*M) defective)

defects/lean4/Makefile

@@ -0,0 +1,19 @@
+# lean4 patch test + bench runner
+# Targets: all test bench clean
+
+PYTHON    := python3
+TEST_FILE := tests/test-lean4-cwe407.py
+BENCH_DIR := bench
+
+.PHONY: all test bench clean
+
+all: test bench
+
+test:
+	$(PYTHON) $(TEST_FILE)
+
+bench:
+	$(PYTHON) $(BENCH_DIR)/run_all.py
+
+clean:
+	rm -rf tests/__pycache__ bench/__pycache__ __pycache__