* fix(docker): keep runtime data out of the build context
backend/Dockerfile copies the backend tree wholesale, and .dockerignore did
not exclude the directories a running DeerFlow writes: DEER_FLOW_HOME
(backend/.deer-flow by default) and the local sandbox workspace root
(backend/sandbox).
Two consequences. Building on a host that has run DeerFlow bakes that state
into the image, including .jwt_secret and the sqlite user database. And once
the Gateway container has created directories owned by root, the build client
can no longer read them and the build fails outright:
target gateway: failed to solve: error from sender:
open .../.deer-flow/users/<uuid>/integrations/lark-cli: permission denied
Neither directory has tracked content, so excluding them costs the build
nothing. The new test pins both that the runtime paths are excluded and that
real build inputs still are not.
* fix(docker): exclude nested env files from builds
