fix: harden concurrency limits and high-RPM runtime paths

Bound request, stream, queue, and shutdown resource lifetimes. Reduce scheduler and Redis hot-path work and isolate database maintenance. Include regression coverage, load probes, and concurrency audit results.

apps/aether-tunnel/src/main.rs

@@ -53,8 +53,13 @@ fn build_command() -> clap::Command {
         .subcommand_negates_reqs(true)
 }
 
+fn main() -> anyhow::Result<()> {
+    let _log_shutdown = aether_runtime::LogShutdownGuard::new();
+    run()
+}
+
 #[tokio::main]
-async fn main() -> anyhow::Result<()> {
+async fn run() -> anyhow::Result<()> {
     rustls::crypto::ring::default_provider()
         .install_default()
         .map_err(|_| anyhow::anyhow!("Failed to install rustls CryptoProvider"))?;