build: add Makefile with standard targets

- Introduce Makefile supporting build, test, install, uninstall, clean
- Add variables for PREFIX and DESTDIR
- Update README.md with Makefile usage instructions

Makefile

@@ -0,0 +1,38 @@
+# Makefile for passwdgen
+# Supports: build, test, install, uninstall, clean
+# Vars: PREFIX=/usr/local make install
+#       DESTDIR=/tmp/staging make install
+
+PREFIX ?= /usr/local
+BUILD_DIR ?= build
+JOBS ?= $(shell sysctl -n hw.ncpu 2>/dev/null || echo 4)
+
+.PHONY: all build test clean install uninstall
+
+all: build
+
+build:
+	cmake -S . -B $(BUILD_DIR) -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release
+	cmake --build $(BUILD_DIR) -j$(JOBS)
+
+test: build
+	ctest --test-dir $(BUILD_DIR) -V
+
+clean:
+	rm -rf $(BUILD_DIR)
+
+install: build
+	mkdir -p $(DESTDIR)$(PREFIX)/bin
+	cp $(BUILD_DIR)/passwdgen $(DESTDIR)$(PREFIX)/bin/passwdgen
+	chmod 755 $(DESTDIR)$(PREFIX)/bin/passwdgen
+	mkdir -p $(DESTDIR)$(PREFIX)/lib
+	cp $(BUILD_DIR)/libpasswdgen_lib.a $(DESTDIR)$(PREFIX)/lib/libpasswdgen_lib.a
+	chmod 644 $(DESTDIR)$(PREFIX)/lib/libpasswdgen_lib.a
+	mkdir -p $(DESTDIR)$(PREFIX)/include
+	cp include/passwdgen.h $(DESTDIR)$(PREFIX)/include/passwdgen.h
+	chmod 644 $(DESTDIR)$(PREFIX)/include/passwdgen.h
+
+uninstall:
+	rm -f $(DESTDIR)$(PREFIX)/bin/passwdgen
+	rm -f $(DESTDIR)$(PREFIX)/lib/libpasswdgen_lib.a
+	rm -f $(DESTDIR)$(PREFIX)/include/passwdgen.h

README.md

@@ -36,3 +36,21 @@ or directly:
 ```bash
 ./tests/passwdgen_test
 ```
+
+
+
+## Makefile
+
+Now supports standard targets via `Makefile`:
+
+```bash
+make          # alias for build (Release)
+make test     # build + run tests
+sudo make install  # to /usr/local/bin, /lib, /include
+make uninstall     # remove installed files
+make clean    # rm -rf build/
+```
+
+Variables:
+- `PREFIX=/opt/myprefix make install`
+- `DESTDIR=/tmp/root PREFIX=/usr make install` (packaging)