Add lib/api/routes/source_docs.js: scoped POST under a resource,
get/patch/delete by id, and POST /:id/resync as a Plan 3 stub gated
by ENABLE_RESYNC (503 by default, 202 once workers ship). upstream_url
is required by the DB so the zod schema enforces it.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
