feat: add protocol comparison docs, P2P crate, production audit, and design fixes

Add comprehensive documentation comparing quicnprotochat against classical
chat protocols (IRC+SSL, XMPP, Telegram) with diagrams and attack scenarios.
Promote comparison pages to top-level sidebar section. Include P2P transport
crate (iroh), production readiness audit, CI workflows, dependency policy,
and continued architecture improvements across all crates.

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

crates/quicnprotochat-client/tests/e2e.rs

@@ -1,3 +1,6 @@
+// cargo_bin! only works for current package's binary; we spawn quicnprotochat-server from another package.
+#![allow(deprecated)]
+
 use std::{path::PathBuf, process::Command, time::Duration};
 
 use assert_cmd::cargo::cargo_bin;
@@ -5,9 +8,14 @@ use portpicker::pick_unused_port;
 use tempfile::TempDir;
 use tokio::time::sleep;
 
+// Required by rustls 0.23 when QUIC/TLS is used from this process (e.g. client in test).
+fn ensure_rustls_provider() {
+    let _ = rustls::crypto::ring::default_provider().install_default();
+}
+
 use quicnprotochat_client::{
-    cmd_create_group, cmd_invite, cmd_join, cmd_ping, cmd_register_state, cmd_send, ClientAuth,
-    connect_node, fetch_wait, init_auth,
+    cmd_create_group, cmd_invite, cmd_join, cmd_ping, cmd_register_state, cmd_send, connect_node,
+    fetch_wait, init_auth, ClientAuth,
 };
 use quicnprotochat_core::IdentityKeypair;
 
@@ -39,6 +47,8 @@ async fn wait_for_health(server: &str, ca_cert: &PathBuf, server_name: &str) ->
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn e2e_happy_path_register_invite_join_send_recv() -> anyhow::Result<()> {
+    ensure_rustls_provider();
+
     let temp = TempDir::new()?;
     let base = temp.path();
     let port = pick_unused_port().expect("free port");
@@ -51,7 +61,7 @@ async fn e2e_happy_path_register_invite_join_send_recv() -> anyhow::Result<()> {
 
     // Spawn server binary.
     let server_bin = cargo_bin("quicnprotochat-server");
-    let mut child = Command::new(server_bin)
+    let child = Command::new(server_bin)
         .arg("--listen")
         .arg(&listen)
         .arg("--data-dir")
@@ -108,12 +118,7 @@ async fn e2e_happy_path_register_invite_join_send_recv() -> anyhow::Result<()> {
         .await?;
 
     local
-        .run_until(cmd_create_group(
-            &alice_state,
-            &server,
-            "test-group",
-            None,
-        ))
+        .run_until(cmd_create_group(&alice_state, &server, "test-group", None))
         .await?;
 
     // Load Bob identity key from persisted state to use as peer key.
@@ -134,13 +139,7 @@ async fn e2e_happy_path_register_invite_join_send_recv() -> anyhow::Result<()> {
         .await?;
 
     local
-        .run_until(cmd_join(
-            &bob_state,
-            &server,
-            &ca_cert,
-            "localhost",
-            None,
-        ))
+        .run_until(cmd_join(&bob_state, &server, &ca_cert, "localhost", None))
         .await?;
 
     // Send Alice -> Bob.