feat(vless): add VLESS+REALITY transport support

Add VLESS over REALITY as a third VPN transport alongside Shadowsocks and AmneziaWG.

- Implement VLESS protocol parser, TCP relay, and REALITY-based TLS server.
- Add x25519 keypair and short ID generation with tests.
- Add MMDB manager for automatic download and daily update of GeoIP databases.
- Integrate VLESS server lifecycle into main serve command and API handlers.
- Add CLI subcommands: vless keygen, vless info, vless share.
- Extend store with VLESSKeyData and REALITY server keys persistence.
- Update config with vless section and MMDB URL/cache/auto-update settings.

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Initial commit: Shadowsocks + AmneziaWG VPN server

Single-binary Go replacement for the Outline VPN server stack.
Supports Shadowsocks (via outline-ss-server library) and AmneziaWG
with HTTP/3 mux for DPI resistance (MuxBind shares UDP port between
AWG and a real QUIC/HTTP/3 server with Let's Encrypt).

Includes systemd unit, install script for Ubuntu, and REST API
compatible with the Outline Manager.

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