keep historic typo in value but not in constant

We need to keep the historic typo in the value ("substition"), but there
is no reason to keep it in the constant.

move handler methods into ParserMode classes and rename Handler

Each ParserMode class now implements handle() from ModeInterface,
containing the token handling logic that previously lived as individ

move handler methods into ParserMode classes and rename Handler

Each ParserMode class now implements handle() from ModeInterface,
containing the token handling logic that previously lived as individual
methods on Doku_Handler.

The Handler class (formerly Doku_Handler) is the single dispatch point:
Lexer passes tokens to Handler::handleToken() which routes to mode
objects, plugins, or returns false. The Lexer only tokenizes and
resolves mapHandler aliases.

Key changes:
- Add handle() to ModeInterface, implemented by all mode classes
- Move Doku_Handler to dokuwiki\Parsing\Handler namespace
- File extends Code (shared parsing via $type property)
- Quotes uses mapHandler() + Handler::getModeName() for sub-modes
- Media::parseMedia() replaces Doku_Handler_Parse_Media()
- Code::parseHighlightOptions() replaces parse_highlight_options()
- Per-parse state (footnote, doublequote) stays on Handler
- Deprecated wrappers kept for base/header/internallink/media
- Class alias and rector rules added for backward compatibility

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introduce ModeRegistry to encapsulate parser mode categories

Replace the global $PARSER_MODES definition in inc/parser/parser.php
with a ModeRegistry singleton that initializes and manages the mode

introduce ModeRegistry to encapsulate parser mode categories

Replace the global $PARSER_MODES definition in inc/parser/parser.php
with a ModeRegistry singleton that initializes and manages the mode
categories. The global array is still populated for backward
compatibility with plugins that access it directly.

Mode constructors now use ModeRegistry::getModesForCategories()
instead of accessing the global directly. p_get_parsermodes() and
p_sort_modes() are moved to inc/deprecated.php as thin wrappers.

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code style: line breaks

moved all parsing related namespaces to their own