feat: initial release

Fixed volume steps for Bluetooth audio devices on PipeWire. Corrects the
coarse internal volume grid of devices such as AirPods Pro (16 AVRCP steps,
6.25 % per swipe) to the desktop's own step size.

The device grid is measured per device; the desktop step size is read from
Plasma. English and German messages.

Makefile

@@ -0,0 +1,21 @@
+PREFIX  ?= /usr
+DESTDIR ?=
+
+BINDIR  = $(DESTDIR)$(PREFIX)/bin
+UNITDIR = $(DESTDIR)$(PREFIX)/lib/systemd/user
+
+.PHONY: install uninstall check
+
+install:
+	install -Dm755 bt-volume-step $(BINDIR)/bt-volume-step
+	install -Dm644 systemd/bt-volume-step.service \
+		$(UNITDIR)/bt-volume-step.service
+	sed -i 's|^ExecStart=.*|ExecStart=$(PREFIX)/bin/bt-volume-step|' \
+		$(UNITDIR)/bt-volume-step.service
+
+uninstall:
+	rm -f $(BINDIR)/bt-volume-step
+	rm -f $(UNITDIR)/bt-volume-step.service
+
+check:
+	python3 tests/test_bt_volume_step.py