Refactor program configuration types into a dedicated public `config`
module under `mingling_core`, making `StructuralRendererSetting`
accessible via `mingling_core::config` instead of the crate root.

Update all internal references and setup modules to use the new
`config::` path convention.

Mark all source files with a comment indicating they are not optimized
for documentation purposes.

Add `#[allow(clippy::future_not_send)]` to chain invocation methods and
clarify Send requirements for `exec` bounds.

Replace bool-based settings with enums, refine visibility and
signatures, and standardize `Self` usage across the crate.

- Introduce `ErrorOutput`, `RenderOutput`, `PanicSilence`, `Verbosity`,
  `ColorOutput`, and `ProgressOutput` enums for clearer configuration
  semantics
- Make `GlobalResources`, `ProgramCell`, and
  `split_input`/`split_input_string` public
- Change hook info parameters to accept references and
  `split_input_string` to take `&str`
- Apply `Self` shorthand throughout implementations and add
  `#[must_use]` attributes where appropriate
- Enable strict clippy lints with targeted allowances

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 `#![deny(missing_docs)]` across multiple crates and fill in
documentation for all public items, including struct fields, enum
variants, trait methods, and proc macros.  Also mark two shell scripts
as executable.