Adopt the standard tooling from sneak/prompts: the Makefile and script/
entrypoints, lint and test stages in one Dockerfile, the canonical lint
config, the CI workflow and the formatter settings. Change the module
path to sneak.berlin/go/dcf.
Fix the lint findings in pkg/dcf in place. DCFStore becomes Store and
DCFObject becomes Object. One behaviour changes: an error listing mount
points is now returned, where a typo used to drop it.
Replace the placeholder test with real tests. Move the README into the
required sections. make build now compiles the library; it pointed at a
command that does not exist.
Model: opus-5-5
