fix: apply TimeoutLayer to gateway router for request timeouts

Add tower-http TimeoutLayer with the existing REQUEST_TIMEOUT_SECS (30s)
constant and 408 Request Timeout status code. Previously, the constant
was defined but no timeout middleware was applied, allowing slow
requests to hold connections indefinitely (slow-loris risk).

Closes #60

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/gateway/mod.rs

@@ -23,7 +23,9 @@ use axum::{
 };
 use std::net::SocketAddr;
 use std::sync::Arc;
+use std::time::Duration;
 use tower_http::limit::RequestBodyLimitLayer;
+use tower_http::timeout::TimeoutLayer;
 
 /// Maximum request body size (64KB) — prevents memory exhaustion
 pub const MAX_BODY_SIZE: usize = 65_536;
@@ -163,8 +165,6 @@ pub async fn run_gateway(host: &str, port: u16, config: Config) -> Result<()> {
     };
 
     // Build router with middleware
-    // Note: Body limit layer prevents memory exhaustion from oversized requests
-    // Timeout is handled by tokio's TcpListener accept timeout and hyper's built-in timeouts
     let app = Router::new()
         .route("/health", get(handle_health))
         .route("/pair", post(handle_pair))
@@ -172,7 +172,11 @@ pub async fn run_gateway(host: &str, port: u16, config: Config) -> Result<()> {
         .route("/whatsapp", get(handle_whatsapp_verify))
         .route("/whatsapp", post(handle_whatsapp_message))
         .with_state(state)
-        .layer(RequestBodyLimitLayer::new(MAX_BODY_SIZE));
+        .layer(RequestBodyLimitLayer::new(MAX_BODY_SIZE))
+        .layer(TimeoutLayer::with_status_code(
+            StatusCode::REQUEST_TIMEOUT,
+            Duration::from_secs(REQUEST_TIMEOUT_SECS),
+        ));
 
     // Run the server
     axum::serve(listener, app).await?;

src/security/secrets.rs

@@ -241,7 +241,7 @@ fn hex_encode(data: &[u8]) -> String {
 
 /// Hex-decode a hex string to bytes.
 fn hex_decode(hex: &str) -> Result<Vec<u8>> {
-    if hex.len() % 2 != 0 {
+    if !hex.len().is_multiple_of(2) {
         anyhow::bail!("Hex string has odd length");
     }
     (0..hex.len())

src/tools/browser.rs

@@ -366,6 +366,7 @@ impl BrowserTool {
 }
 
 #[async_trait]
+#[allow(clippy::too_many_lines)]
 impl Tool for BrowserTool {
     fn name(&self) -> &str {
         "browser"