ollie/.plan.md

Plan: Remove httpgw + webui

1. Remove cmd/ollie-httpgw/ directory ✓ (git rm)
2. Remove webui/ submodule ✓ (git rm)
3. Update justfile ✓
4. Update README.md ✓
5. Update doc/ARCHITECTURE.md ✓
6. Update doc/EVOLUTION.md ✓
7. Update doc/USAGE.md ✓
8. Update AGENTS.md — repo layout, build system, testing, architecture, key files, submodule workflow ← IN PROGRESS
9. Commit + push