Add Makefile with install target for distro packaging

Adds build, install, and uninstall targets with standard PREFIX/DESTDIR
support. Installs binary, desktop file, metainfo, GSettings schema,
app icons, scalable action icons (outlay + tabler), and bundled fonts.
This allows distro packagers (Nix, Arch, Debian, etc.) to properly
install icons alongside the binary so GTK can find them at runtime.

Makefile

@@ -0,0 +1,58 @@
+PREFIX ?= /usr/local
+DESTDIR ?=
+BINDIR = $(PREFIX)/bin
+DATADIR = $(PREFIX)/share
+
+ICON_DATA = outlay-gtk/data/icons
+DESKTOP_FILE = outlay-gtk/data/com.outlay.app.desktop
+METAINFO_FILE = outlay-gtk/data/com.outlay.app.metainfo.xml
+SCHEMA_FILE = outlay-gtk/data/com.outlay.app.gschema.xml
+
+.PHONY: build install uninstall
+
+build:
+	cargo build --release -p outlay-gtk
+
+install: build
+	install -Dm755 target/release/outlay-gtk $(DESTDIR)$(BINDIR)/outlay-gtk
+
+	# Desktop file
+	install -Dm644 $(DESKTOP_FILE) $(DESTDIR)$(DATADIR)/applications/com.outlay.app.desktop
+
+	# AppStream metainfo
+	install -Dm644 $(METAINFO_FILE) $(DESTDIR)$(DATADIR)/metainfo/com.outlay.app.metainfo.xml
+
+	# GSettings schema
+	install -Dm644 $(SCHEMA_FILE) $(DESTDIR)$(DATADIR)/glib-2.0/schemas/com.outlay.app.gschema.xml
+
+	# App icons (raster sizes)
+	for size_dir in $(ICON_DATA)/hicolor/*/apps; do \
+		size=$$(basename "$$(dirname "$$size_dir")"); \
+		for icon in "$$size_dir"/com.outlay.app.*; do \
+			[ -f "$$icon" ] || continue; \
+			install -Dm644 "$$icon" $(DESTDIR)$(DATADIR)/icons/hicolor/$$size/apps/$$(basename "$$icon"); \
+		done; \
+	done
+
+	# Scalable action icons (outlay custom + tabler)
+	for svg in $(ICON_DATA)/hicolor/scalable/actions/outlay-*.svg \
+	           $(ICON_DATA)/hicolor/scalable/actions/tabler-*.svg; do \
+		[ -f "$$svg" ] || continue; \
+		install -Dm644 "$$svg" $(DESTDIR)$(DATADIR)/icons/hicolor/scalable/actions/$$(basename "$$svg"); \
+	done
+
+	# Bundled fonts
+	for ttf in outlay-gtk/data/fonts/*.ttf; do \
+		[ -f "$$ttf" ] || continue; \
+		install -Dm644 "$$ttf" $(DESTDIR)$(DATADIR)/fonts/outlay/$$(basename "$$ttf"); \
+	done
+
+uninstall:
+	rm -f $(DESTDIR)$(BINDIR)/outlay-gtk
+	rm -f $(DESTDIR)$(DATADIR)/applications/com.outlay.app.desktop
+	rm -f $(DESTDIR)$(DATADIR)/metainfo/com.outlay.app.metainfo.xml
+	rm -f $(DESTDIR)$(DATADIR)/glib-2.0/schemas/com.outlay.app.gschema.xml
+	rm -rf $(DESTDIR)$(DATADIR)/icons/hicolor/*/apps/com.outlay.app.*
+	rm -rf $(DESTDIR)$(DATADIR)/icons/hicolor/scalable/actions/outlay-*.svg
+	rm -rf $(DESTDIR)$(DATADIR)/icons/hicolor/scalable/actions/tabler-*.svg
+	rm -rf $(DESTDIR)$(DATADIR)/fonts/outlay