1. The changes introduce a new `DependencyError` class in `kamal/cli.rb` alongside other error classes like `BootError` and `HookError`. This new error class will be used to handle dependency-related failures.
2. In `kamal/cli/base.rb`, a new method `ensure_docker_installed` is added which checks for Docker and buildx plugin installation locally. It raises the new `DependencyError` with appropriate messages if either Docker or buildx plugin are not found, replacing similar functionality that was previously scattered elsewhere.
3. The `kamal/cli/build.rb` file is modified to use the new `ensure_docker_installed` method instead of the removed `verify_local_dependencies` method. The error handling is now consistent, using `DependencyError` instead of `BuildError` for dependency-related failures.
4. The `kamal/cli/registry.rb` file now includes a call to `ensure_docker_installed` at the start of the login method, ensuring Docker is available before attempting registry operations.
5. The `kamal/commands/base.rb` file adds a new public method `ensure_docker_installed` that combines checks for both Docker and buildx plugin installation, moving this functionality from the Builder class.
6. The `kamal/commands/builder.rb` file is simplified by removing the `ensure_local_dependencies_installed` method and related private methods, as this functionality has been moved to the base commands class.
7. Test files are updated to reflect these changes, with `build_test.rb` now expecting `DependencyError` instead of `BuildError` for dependency failures, and `registry_test.rb` adding a new test case for Docker dependency checking during login.