Replace skip marker files with top-level module config #17

Problem

The Go module currently uses marker files to skip work:

• .dagger-skip-go-lint
• .dagger-skip-go-test
• .dagger-skip-go-generate

Those sentinels are discovered from the workspace tree and ancestor paths. This works, but it scatters module behavior across filesystem marker files, makes configuration harder to inspect, and couples skip behavior to extra workspace globs.

Proposal

Replace the marker-file approach with a top-level module configuration for lint/test/generate skip behavior.

The exact API/config shape needs design, but it should let callers configure skip behavior centrally for module roots or subtrees instead of adding sentinel files to the source tree.

Acceptance criteria

• Lint/test/generate skip behavior can be configured from a top-level module config.
• modules, lintAll, testAll, generateAll, and per-module skip introspection use the same config source.
• It remains possible to skip lint, test, and generate independently.
• The behavior for module roots and nested module trees is covered by e2e tests.
• Existing marker files are either migrated, deprecated with compatibility, or removed deliberately as part of the change.