- README: refresh "what it does", "architecture at a glance", "containers"
table, "configuration", "storage layout" (with usage_type→bucket
routing table), and add "documentation" section pointing to
ARCHITECTURE / HANDOVER / DEVELOP / CLAUDE.
- DEVELOP: add the developer-facing guide that was previously only in
CLAUDE.md. Covers code layout, the Settings singleton, conventions
(DB / Storage / Auth / Permission gates / Outbox / async-sync
signatures), local dev workflow, common tasks (adding a DAG endpoint,
env var, MySQL table, RustFS bucket, schedule node type), tests
status, and a troubleshooting section with the four real bugs hit
this session (greenlet, MySQL, Jupyter 401, Schedule not advancing).