Make `StructuralData` and `StructuralDataSealed` generic over a program
collector type to bypass the orphan rule for `group_structural!`. This
enables external types to implement `StructuralData<crate::ThisProgram>`
without violating coherence.

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.

Introduce a `Routable` trait with `to_chain` and `to_render`
methods, replacing direct `Grouped` usage in the `route!` macro
so error branches correctly route through the rendering pipeline

Migrate `mingling_core::pathf` into `mingling_core::builds::pathf` and
re-export from `mingling::build`.  Update all references from
`mingling::builds` and `mingling::pathf` to `mingling::build`.

Add `PathfinderConfig` struct to control dispatch tree extraction,
and wire `use_dispatch_tree` through `DispatcherPattern`,
`init_with_config`,
and `analyze_and_build_type_mapping_for`. Expose config and wrapper
from `mingling_core` under the `pathf` feature.

Add `mingling_pathf` sub-crate and `pathf` feature for automatic
resolution of Mingling type module paths at build time. Scans source
files, identifies macro invocations via pattern matchers, and generates
mapping files consumed by `gen_program!()`.

Introduce `StructuralData` sealed trait and `pack_structural!` /
`group_structural!` / `derive(StructuralData)` macros to control
structured rendering separately from grouping. `Groupped` no longer
requires `Serialize`.