feat: Implement virtual hosting for multi-domain Gemini server

- Add hostname-based request routing for multiple capsules per server
- Parse virtual host configs from TOML sections ([hostname])
- Implement per-host certificate and content isolation
- Add comprehensive virtual host testing and validation
- Update docs and examples for multi-host deployments

This enables Pollux to serve multiple Gemini domains from one instance,
providing the foundation for multi-tenant Gemini hosting.

src/request.rs

@@ -6,6 +6,7 @@ pub enum PathResolutionError {
     NotFound,
 }
 
+#[allow(dead_code)]
 pub fn parse_gemini_url(request: &str, hostname: &str, expected_port: u16) -> Result<String, ()> {
     if let Some(url) = request.strip_prefix("gemini://") {
         let host_port_end = url.find('/').unwrap_or(url.len());