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-p2p/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name        = "quicnprotochat-p2p"
+version     = "0.1.0"
+edition     = "2021"
+description = "P2P transport layer for quicnprotochat using iroh."
+license     = "MIT"
+
+[dependencies]
+iroh        = "0.96"
+tokio       = { workspace = true }
+tracing     = { workspace = true }
+anyhow      = { workspace = true }