test: add BATS test suite (79 tests)

- tests/common.bats: PROJECT_ROOT detection, is_cmd, timestamp, data_dir,
  logging functions, color handling, require_root
- tests/detect.bats: GPU sysfs reads with mock sysfs tree, kernel param
  parsing (word boundary, dot escaping, edge positions), recommended
  GTT/pages computation (64GB, 128GB, tiny, zero), firmware bad detection,
  stack detection
- tests/format.bats: human_bytes (0, KiB, MiB, GiB boundaries, 64GiB),
  human_mib (sub-GiB, exact-GiB, recommended values, empty input)
- tests/benchmark_compare.bats: improvement/regression display, empty
  results, missing files, usage output, config change detection
- tests/log_metrics.bats: CSV header, data format, field count, input
  validation, unknown argument handling
- tests/test_helper.sh: mock sysfs tree builder, bats-assert/support setup

Makefile: add 'make test' target

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Makefile

@@ -1,4 +1,4 @@
-.PHONY: help audit audit-full monitor monitor-simple benchmark benchmark-baseline benchmark-compare optimize verify
+.PHONY: help audit audit-full monitor monitor-simple benchmark benchmark-baseline benchmark-compare optimize verify test
 
 help: ## Show available commands
 	@echo "Strix Halo Optimization Toolkit"
@@ -56,3 +56,7 @@ verify: ## Post-optimization verification checklist
 
 rollback: ## Rollback optimizations
 	@bash scripts/optimize/rollback.sh
+
+# --- Tests ---
+test: ## Run BATS test suite
+	@bats tests/