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.

Cargo.toml

@@ -13,6 +13,7 @@ clap = { version = "4.0", features = ["derive"] }
 path-security = "0.2"
 toml = "0.8"
 serde = { version = "1.0", features = ["derive"] }
+urlencoding = "2.1"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter", "ansi"] }
 time = "0.3"