Add a Makefile, so one command is the whole check

Verifying a change meant four invocations — gofmt, go vet, go build, go
test — and remembering the order. `make` is all of them with one exit code.

gofmt needs the wrapper: it reports offending files on stdout and still
exits 0, so a bare `gofmt -l .` in a target would never fail the build.

Makefile

@@ -0,0 +1,24 @@
+# One command before committing: make
+#
+# gofmt is first because a formatting failure is the cheapest to fix, and it is the only check that
+# needs a wrapper — gofmt reports offending files on stdout and still exits 0.
+.POSIX:
+.PHONY: check fmt vet test build run
+
+check: fmt vet test
+
+fmt:
+	@out=$$(gofmt -l .); test -z "$$out" || { echo "not gofmt'd:"; echo "$$out"; exit 1; }
+
+vet:
+	go vet ./...
+
+test:
+	go test ./...
+
+build:
+	go build -o levyraati26-go .
+
+# Templates and migrations are embedded, so seeing a change means rebuilding.
+run: build
+	./levyraati26-go