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>

docs/src/SUMMARY.md

@@ -4,6 +4,13 @@
 
 ---
 
+# Why quicnprotochat?
+
+- [Comparison with Classical Chat Protocols](design-rationale/protocol-comparison.md)
+- [Why This Design, Not Signal/Matrix/...](design-rationale/why-not-signal.md)
+
+---
+
 # Getting Started
 
 - [Prerequisites](getting-started/prerequisites.md)
@@ -60,7 +67,6 @@
 # Design Rationale
 
 - [Design Decisions Overview](design-rationale/overview.md)
-- [Why This Design, Not Signal/Matrix/...](design-rationale/why-not-signal.md)
 - [ADR-002: Cap'n Proto over MessagePack](design-rationale/adr-002-capnproto.md)
 - [ADR-004: MLS-Unaware Delivery Service](design-rationale/adr-004-mls-unaware-ds.md)
 - [ADR-005: Single-Use KeyPackages](design-rationale/adr-005-single-use-keypackages.md)
@@ -80,6 +86,7 @@
 # Roadmap and Research
 
 - [Milestone Tracker](roadmap/milestones.md)
+- [Phase 2 + M4–M6 Roadmap](roadmap/phase2-and-m4-m6.md)
 - [Production Readiness WBS](roadmap/production-readiness.md)
 - [Auth, Devices, and Tokens](roadmap/authz-plan.md)
 - [1:1 Channel Design](roadmap/dm-channels.md)