v0.5.3

PDFToolkit now shares one documentation site at https://pdftoolkit.github.io/,
with dedicated entry points for the core, PDF reader, image converters and font
converters. The guides, tutorials, API exporter, site generator and assets live
in their dedicated repository.

The core retains its PHP objects and writer, executable examples, fixtures,
original Adobe PDFs and specification catalogues. The old /pdf/ site preserves
HTML navigation, queries, fragments and real binary downloads through a validated
compatibility deployment.

Development dependencies are locked to the published optional-module 0.1.4
releases. Shared API and examples use exact released source commits. Installing
the core still installs no optional module.

PHP 8.3 remains the minimum version, with CI on 8.3, 8.4 and 8.5. This is a
documentation and packaging update with no PHP API change.

See the changelog.