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>

deny.toml

@@ -0,0 +1,29 @@
+# cargo-deny configuration for license compatibility and duplicate detection.
+# See https://embarkstudios.github.io/cargo-deny/
+
+[advisories]
+db-path = "~/.cargo/advisory-db"
+db-urls = ["https://github.com/rustsec/advisory-db"]
+vulnerability = "deny"
+unmaintained = "warn"
+yanked = "deny"
+notice = "warn"
+
+[bans]
+multiple-versions = "warn"
+wildcards = "allow"
+highlight = "all"
+
+[licenses]
+unlicensed = "deny"
+allow = ["MIT", "Apache-2.0", "BSD-2-Clause", "BSD-3-Clause"]
+deny = []
+copyleft = "warn"
+default = "deny"
+allow-osi-fsf-free = "both"
+
+[sources]
+unknown-registry = "deny"
+unknown-git = "deny"
+allow-registry = ["https://github.com/rust-lang/crates.io-index"]
+allow-git = []