BREAKING CHANGE: Replace the `build`/`builds` feature system with
compile-time macro-driven generation. `gen_program!()` now automatically
invokes `build_comp!()` and `build_pathf!()` when the `comp`/`pathf`
features are enabled, eliminating the need for `build.rs` and
`[build-dependencies]` blocks.

This removes the `build` feature, the `mingling::build` module, and all
related build-time API functions. Completion scripts are now written to
`{target_directory}/mingling/` instead of `target/release/`. The
`mingling_cli` uses `build_comp!("mling")` for its custom binary name.

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.

Support file-level lint checks via `check_file` in lint registry
template.

generation

Introduce `metadata` and `mlint` subcommands, wire up `cargo_metadata`
for manifest analysis, and enable procedural macro support in editors