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/control

@@ -0,0 +1,26 @@
+Source: naas
+Section: net
+Priority: optional
+Maintainer: Ole-Morten Duesund <olemd@glemt.net>
+Build-Depends: debhelper-compat (= 13), cargo | rustup, rustc | rustup
+Standards-Version: 4.6.0
+Homepage: https://kode.naiv.no/naas
+Vcs-Git: https://kode.naiv.no/naas.git
+Vcs-Browser: https://kode.naiv.no/naas
+
+Package: naas
+Architecture: any
+Depends: ${shlibs:Depends}, ${misc:Depends}, systemd
+Description: No as a Service - HTTP service that always says "no"
+ NaaS (No as a Service) is a lightweight HTTP service written in pure Rust
+ that always responds with "no" in various formats including plain text,
+ JSON, XML, YAML, and boolean.
+ .
+ Features include:
+  - Minimal dependencies (pure Rust, standard library only)
+  - Multiple response formats
+  - Mobile-responsive web frontend
+  - CORS support
+  - Health check endpoint
+  - Optimized for small binary size (~1MB)
+  - Container-ready with health checks