Add docs/solutions/architecture-patterns/dual-repo-submodule-workflow.md
covering the outer-repo + user/ submodule structure, when to bump the pin
(cross-repo feature boundaries, not routine content), the reachable/push-first
rules, and the worktree + per-worktree dev-server flow. Update CLAUDE.md's
folder explanation and add a "Dual-repo submodule structure" section.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
