Migration from legacy helpers

The compatibility methods below remain callable unless noted otherwise, but new code should use their replacements. They can be removed in the next major release after downstream callers have migrated.

Legacy API	Replacement
`Format::search_wizard()`	`Format::search_clause()` with PDO bindings
`Format::in_wizard()`	`Format::in_clause()` with PDO bindings
`Format::pre()`	`Format::debug()`, emitted by the application when appropriate
`Format::array_to_string()`	PHP’s `implode()`
`Format::fullname()`	String interpolation
`Validation::comma()`	An explicit `str_replace()` at the input boundary
`Validation::clear_number()`	Explicit validation followed by an integer cast
`Password::strength()`	`Password::meets_policy()` or a maintained estimator
`Password::encode()` / `decode()`	Base64 functions in an encoding component
`Password::digest()` / `set_method()`	`Password::hash()` for passwords; PHP’s `hash()` for checksums
`Math::even_or_odd()`	`Math::by_parity()` with an explicit index
`Math::iterate()` and iterator accessors	A local counter
`File::read_file_contents()`	`File::read_csv()`
`File::force_download()`	`File::prepare_download()` plus an application response
`Export::export_file()`	`Export::build()` or `Export::save()`
`Website` keywords state	Omit it; search engines ignore meta keywords
`User_Agent`	Feature detection, Client Hints, or a maintained parser

Directory_Lister::listing() is now data-only. It no longer prints debug HTML when print is supplied and no longer adds an open anchor to each file row.

The ignored cURL binary_transfer response option was removed because its PHP constant is deprecated. Email::show() and Email::mailto() now return safe HTML directly rather than generating calls to document.write().