Add `Metadata<B>` trait and `#[metadata(Entry)]` attribute macro
to attach arbitrary, compile-time-typed metadata to entries.
Implement `ProgramCollect::get_metadata<T>()` for runtime retrieval,
backed by a global registry populated by `register_metadata!`.

Extend `pathf` with `MetadataPattern` to resolve metadata types
across modules at build time. Add two examples demonstrating
metadata usage with and without pathf integration.

Rename the internal fallback type and its associated `ProgramCollect`
plumbing from `ErrorDispatcherNotFound`/`build_dispatcher_not_found` to
`EntryFallback`/`build_entry_fallback`, along with the generated enum
variant and pack type. Update all documentation, examples, and tests
accordingly.

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

Add a new `#[command]` attribute macro (feature-gated behind
`extra_macros`) that converts a plain function with a `Vec<String>`
parameter into a fully wired Mingling command. The macro generates a
`dispatcher!` call, a `#[chain]` wrapper, and a hidden module
re-exporting
all generated types.

Also add `CommandPattern` to the pathf pattern analyzer to recognize
`#[command]`-annotated functions and track their generated hidden
modules.

pipeline error routing