chore: add Makefile with check/fmt/clippy/test/fix targets; apply rustfmt

Makefile

@@ -0,0 +1,28 @@
+.DEFAULT_GOAL := check
+
+# Run the full local check suite — same order as CI would.
+check: fmt-check clippy test
+	@echo "✅ All checks passed"
+
+# Apply rustfmt to all files.
+fmt:
+	cargo fmt
+
+# Check formatting without modifying files (CI-safe).
+fmt-check:
+	cargo fmt --check
+
+# Run Clippy and treat warnings as errors.
+clippy:
+	cargo clippy -- -D warnings
+
+# Run the test suite.
+test:
+	cargo test
+
+# Apply fmt + clippy auto-fixes in one shot.
+fix:
+	cargo fmt
+	cargo clippy --fix --allow-dirty --allow-staged
+
+.PHONY: check fmt fmt-check clippy test fix