feat(awgen): add AmneziaWG configuration generator package

Package alex/awgen (offline, stateless Rust CLI for AmneziaWG configs) from
the upstream Gitea repository. Source is fetched with fetchFromGitea and
pinned to the v0.1 tag; the cargo dependency hash is pinned as well.

Also list the package in the README package table and project tree.

README.md

@@ -13,6 +13,7 @@ A custom Nix overlay and flake providing additional packages not found in upstre
 | Package | Description | Category |
 |---------|-------------|----------|
 | `awg-tool` | CLI for AmneziaWG self-hosting — generates 1.0/1.5/2.0/3.0 obfuscation parameters, exports .conf and vpn:// configs, installs servers over SSH | Networking |
+| `awgen` | Offline CLI for AmneziaWG configurations — harmonises native .conf and vpn:// inputs, generates client participants and tunnels, and analyses obfuscation | Networking |
 | `aionui` | Free, open-source, Cowork app with AI Agents | AI Coding Agents |
 | `codeaf` | Coding harness and software factory for open models: hand work off, then watch every project from one terminal | AI Coding Agents |
 | `container-use` | Containerized environments for coding agents | AI Coding Agents |
@@ -211,6 +212,7 @@ nix-overlay/
 │   └── shared-nixpkgs.nix      # Dependency-sharing overlay
 ├── packages/                    # Package definitions
 │   ├── awg-tool/               # AmneziaWG parameter generation and SSH deployment CLI
+│   ├── awgen/                  # Offline AmneziaWG configuration harmoniser and generator
 │   ├── aionui/                 # AionUi - AI Cowork desktop app
 │   ├── codeaf/                 # Coding harness and software factory for open models
 │   ├── container-use/          # Containerized environments for coding agents