Enable the dispatch_tree and comp features to generate
completion scripts during build and register global help
and completion support in the main entry point.

Replace AnyOutput-based dispatch with RendererInvoker in
render_lint_reports_json to improve type safety and clarity.

Update all references across docs, examples, and configuration files to
use the shorter `extras` feature name.

Introduce `might_be_async` as a workspace dependency, add it to
`mingling_core`, and regenerate all Cargo.lock files accordingly.
Multiple examples and test packages also pick up a newly transitive
`equivalent` crate.

Replace the `builds` feature with `build` across the crate, keeping
a backward-compatible alias for the old name.  Update all internal
visibility from `#[doc(hidden)] pub mod` to `pub(crate) mod` and
reorganize the `__private` module into a dedicated `private.rs`.