Add TLS handshake timeout (review #010 C3)

tls_handshake_timeout_secs (default 10s, must be > 0) wraps
tls_acceptor.accept() in tokio::time::timeout so stalled handshakes
(slowloris / crawler slow-handshake vector) can no longer hold an FD +
semaphore permit indefinitely. Config plumbing through FullConfig /
StaticConfig / validation / reload diff + docs.

README.md

@@ -116,6 +116,7 @@ Configuration uses TOML and is split into **static** (requires restart) and
 | `admin_key_path` | `/etc/reverse-proxy/admin-key` | Path to admin Bearer token file (empty string to disable) |
 | `shutdown_timeout_secs` | `30` | Graceful shutdown timeout |
 | `connection_idle_timeout_secs` | `60` | Server-side idle timeout for client TLS connections (prevents FD exhaustion from abandoned connections) |
+| `tls_handshake_timeout_secs` | `10` | Max seconds to complete the TLS handshake; stalled handshakes are closed (prevents slowloris FD/permit exhaustion) |
 | `max_connections` | `1024` | Max concurrent client TLS connections (backpressure via semaphore) |
 | `logging.level` | `"info"` | Log level |
 | `logging.format` | `"text"` | Log format (`"text"` or `"json"`) |