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>

.github/CODEOWNERS

@@ -0,0 +1,15 @@
+# Code owners for quicnprotochat. PRs require review from owners.
+# See https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
+# Replace 'maintainers' with your GitHub user/team handle.
+
+# Default owners for everything in the repo
+* @maintainers
+
+# Crate-specific (uncomment and add handles when you have designated owners)
+# /crates/quicnprotochat-core/     @owner1
+# /crates/quicnprotochat-proto/    @owner1
+# /crates/quicnprotochat-server/   @owner1
+# /crates/quicnprotochat-client/   @owner1
+# /crates/quicnprotochat-p2p/      @owner1
+# /schemas/                        @owner1
+# /docs/                           @owner1