split Parsing\Helpers into per-domain Link / Media / Code classes

add GfmMedia and extend GfmLink with image-as-label form

- New GfmMedia parses `` with the full DokuWiki media-parameter
vocabulary in the URL slot (?100x200, ?right, ?nolink, ?recache,

add GfmMedia and extend GfmLink with image-as-label form

- New GfmMedia parses `` with the full DokuWiki media-parameter
vocabulary in the URL slot (?100x200, ?right, ?nolink, ?recache, …).
Adds `?left`/`?right`/`?center` align keywords shared with DW `{{…}}`
— gives pure-Markdown users a way to align inline images.
- GfmLink now also matches `[](target)` — the GFM equivalent
of `[[target|{{img}}]]`. Detection is post-entry, mirroring
Internallink's `^{{…}}$` check; one mode covers the whole family.
- LinkDispatch trait replaced by Helpers::classifyLink and
Helpers::parseMediaParameters — two pure static methods, shared by
DW and GFM counterparts.
- Entry patterns for GfmLink / GfmMedia simplified (permissive URL slot,
handle-time parsing), following DW's Internallink style.
- GfmSpecTest drives a test-only SpecCompatRenderer that emits bare
<img> / <a> instead of DW's wiki-wrapped HTML, recovering 13 spec
tests that previously failed/skipped only because of renderer shape.

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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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code style: line breaks

moved all parsing related namespaces to their own