Initialize Rust project with Cargo, dependencies, and module skeleton

Set up single-binary reverse-proxy project with all core dependencies
(axum, tokio, hyper, tower, rustls, tokio-rustls, rustls-acme, serde,
toml, arc-swap, tracing, tracing-subscriber, rustls-pemfile,
rustls-pki-types, clap, signal-hook, anyhow, thiserror) pinned to exact
versions. Create module skeleton (config, proxy, tls, rate_limit,
logging, admin, health, shutdown) matching architecture spec.

src/config/validation.rs

@@ -0,0 +1,12 @@
+use anyhow::Result;
+
+use super::dynamic_config::DynamicConfig;
+use super::static_config::StaticConfig;
+
+#[allow(dead_code)]
+pub fn validate_config(
+    _static_config: &StaticConfig,
+    _dynamic_config: &DynamicConfig,
+) -> Result<()> {
+    Ok(())
+}