Add Debian packaging support with configurable binding

- Add complete debian/ packaging structure for .deb creation
- Support BIND_ADDR environment variable (defaults to 0.0.0.0)
- Create /etc/default/naas config file (defaults to localhost binding)
- Systemd service reads from /etc/default/naas
- Package installs but does not auto-enable service
- Upgrades restart service only if already enabled
- Proper user creation and cleanup on install/remove

Key files:
- debian/control: Package metadata with rustup build dependency support
- debian/naas.default: Configuration template for /etc/default/naas
- debian/naas.service: Updated systemd service with EnvironmentFile
- debian/postinst: Creates naas user, restarts on upgrade if enabled
- debian/prerm: Stops service on removal
- debian/postrm: Cleans up user on purge
- src/main.rs: Added BIND_ADDR support for configurable binding

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

debian/rules

@@ -0,0 +1,20 @@
+#!/usr/bin/make -f
+
+%:
+	dh $@
+
+override_dh_auto_build:
+	cargo build --release
+
+override_dh_auto_test:
+	cargo test
+
+override_dh_auto_clean:
+	cargo clean || true
+
+override_dh_auto_install:
+	dh_auto_install
+	# Install config file
+	install -D -m 644 debian/naas.default debian/naas/etc/default/naas
+	# Install systemd service
+	install -D -m 644 debian/naas.service debian/naas/lib/systemd/system/naas.service