Replace `ThisProgram` with `Self` where appropriate and
mark constructors as `#[must_use]` and `const` where possible.
Simplify explicit lifetimes in `ProgramSetup` and `Default`
implementations using elided lifetimes.

Update stdout and error output settings to use explicit `RenderOutput`
and `ErrorOutput` enums, and replace the `confirm` boolean with distinct
`ConfirmationMode`, `InteractionMode`, and `YesAssumption` fields for
clearer control flow.

trait

Remove `Deref<Target=str>` and `render_text:String` in favor of
`render_buffer:Vec<(String, RenderResultMode)>` and an
`immediate_output`
flag. Add `RenderResultMode` enum, `r_eprint!`/`r_eprintln!` macros, and
new buffer manipulation methods (`append_to_buffer`, `eprint`, etc.).
Update `Display` to trim output and remove trailing newline. Migrate all
callers and tests away from `Deref` usage.

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.

enabled

BREAKING CHANGE: Remove `mingling_support` feature from arg-picker
crate. The
`EntryPicker` trait and `corebind` module are now part of the mingling
crate
directly, and `build_pattern1` is now a public method.

Move the inline `remains_arg` definition into a shared public constant
`REMAINS` and update all consumers to import it from the new location.