docs: add Claude Code project guide and verified architecture reference

Contributor-friendly CLAUDE.md with setup, conventions, and architecture
overview. Comprehensive skills/architecture.md verified against actual
codebase covering all 31 source directories, 38+ exports, and major
subsystems (distributed, transactions, neural, CLI, MCP, COW, etc).

Remove CLAUDE.md from .gitignore since the new version is designed
for public contributors.

.gitignore

@@ -52,14 +52,12 @@ temp/
 
 # Planning and instruction files
 plan.md
-CLAUDE.md
 
 # Package files
 *.tgz
 
 # Private/confidential files
 PLAN.md
-CLAUDE.md
 INTERNAL_NOTES.md
 TODO_PRIVATE.md
 *.tar.gz
@@ -81,7 +79,6 @@ models-cache/
 
 # Development planning files (not for commit)
 PLAN.md
-CLAUDE.md
 
 # Backup folders
 backup-*