feat: initial SOCKS5 proxy with chain support

Asyncio-based SOCKS5 server that tunnels connections through
configurable chains of SOCKS5, SOCKS4/4a, and HTTP CONNECT proxies.
Tor integration via standard SOCKS5 hop.

docs/INSTALL.md

@@ -0,0 +1,39 @@
+# s5p -- Installation
+
+## Prerequisites
+
+- Python >= 3.11
+- pip
+- Tor (optional, for Tor-based chains)
+
+## Install
+
+```bash
+cd ~/git/s5p
+python -m venv .venv
+source .venv/bin/activate
+pip install -e .
+```
+
+## Verify
+
+```bash
+s5p --version
+which s5p
+```
+
+## Install Tor (optional)
+
+```bash
+sudo apt install tor
+sudo systemctl enable --now tor
+
+# Verify Tor SOCKS5 port
+ss -tlnp | grep 9050
+```
+
+## Symlink (alternative)
+
+```bash
+ln -sf ~/git/s5p/.venv/bin/s5p ~/.local/bin/s5p
+```