build(debian): add a Debian and Ubuntu package definition

Add a debhelper-free debian/ tree so a .deb can be built with the Go toolchain and dpkg-dev alone. debian/rules compiles the binary with -trimpath and the version from debian/changelog, then stages the binary, the lazyntfy(1) man page, the license, and the README. The package Depends on ca-certificates for TLS to the ntfy server.

debian/rules

@@ -0,0 +1,37 @@
+#!/usr/bin/make -f
+# Debian packaging without debhelper: the Go toolchain builds the binary and
+# the rules stage it by hand. This keeps the build dependencies to just Go.
+
+export CGO_ENABLED = 0
+
+PACKAGE := lazyntfy
+VERSION := $(shell dpkg-parsechangelog -SVersion)
+PKGDIR  := debian/$(PACKAGE)
+
+.PHONY: clean build build-arch build-indep binary binary-arch binary-indep
+
+clean:
+	rm -rf $(PKGDIR) $(PACKAGE)
+	rm -f debian/files
+
+build: build-arch build-indep
+
+build-arch: $(PACKAGE)
+
+build-indep:
+
+$(PACKAGE):
+	go build -trimpath -ldflags "-s -w -X main.version=$(VERSION)" -o $(PACKAGE) ./cmd/$(PACKAGE)
+
+binary: binary-arch binary-indep
+
+binary-arch: build-arch
+	install -d $(PKGDIR)/DEBIAN
+	install -Dm755 $(PACKAGE) $(PKGDIR)/usr/bin/$(PACKAGE)
+	install -Dm644 man/lazyntfy.1 $(PKGDIR)/usr/share/man/man1/lazyntfy.1
+	install -Dm644 LICENSE $(PKGDIR)/usr/share/doc/$(PACKAGE)/copyright
+	install -Dm644 README.md $(PKGDIR)/usr/share/doc/$(PACKAGE)/README.md
+	dpkg-gencontrol -p$(PACKAGE) -P$(PKGDIR)
+	dpkg-deb --build --root-owner-group $(PKGDIR) ..
+
+binary-indep: