Archive V1/V2 source checkouts under archive/v2

The platform is parked pending the V3 redesign. The nine component
checkouts (mcat, mcdoc, mcdsl, mcias, mcns, mcp, mc-proxy, mcr, metacrypt)
move to archive/v2/, still as independent git repos. Documentation stays
where it is; README and CLAUDE.md gain a pointer.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.gitignore

@@ -20,3 +20,6 @@
 /mcr.toml
 /metacrypt.toml
 /.claude/
+
+# V1/V2 source checkouts, archived 2026-09-20. Each is its own git repo.
+/archive/