feat: add mobile image variant sources to pictures

[ArnaudLigny]

This pull request adds support for mobile image variants throughout the codebase, allowing the system to automatically detect and serve mobile-specific image files (e.g., image.mobile.png) using the <picture> element and appropriate media queries. The changes include configuration options for mobile variants, logic to generate mobile <source> elements, and tests to verify the new functionality.

Support for mobile image variants:

• Added mobile_suffix and mobile_media_query configuration options to both config/default.php and tests/fixtures/website/config.yml, enabling specification of mobile image variants and their associated media queries. [1] [2] [3] [4]
• Implemented buildMobileAssetPath and buildMobileSourceAttributes methods in src/Asset/Image.php to construct and handle mobile image variant paths and <source> attributes for responsive images. [1] [2]

Rendering and parsing enhancements:

• Updated src/Converter/Parsedown.php to detect mobile image variants, cache their source attributes, and inject them into the <picture> element alongside dark variants, ensuring correct rendering in markdown. [1] [2] [3] [4] [5]
• Updated src/Renderer/Extension/Core.php to build and include mobile <source> elements in the HTML output for images, using the new configuration options and logic. [1] [2]

Testing:

• Enhanced integration tests in tests/IntegrationTests.php to verify that mobile variant sources are present in the generated HTML with correct media attributes and file paths.

[Copilot]

Pull request overview

This PR adds first-class support for mobile-specific image variants (e.g., image.mobile.png) so Cecil can emit <picture> elements containing additional <source> entries targeting mobile via a configurable media query.

Changes:

• Added mobile_suffix and mobile_media_query configuration for both Markdown-rendered images and Twig html() rendering.
• Implemented mobile-variant path detection and <source> attribute generation for responsive/format variants.
• Extended integration tests + fixtures to validate mobile variant <source> output.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
config/default.php	Adds default configuration options for mobile image variants (pages + layouts).
src/Asset/Image.php	Implements mobile-variant path building and <source> attribute generation.
src/Converter/Parsedown.php	Detects/caches mobile variant sources and injects them into Markdown-generated <picture>.
src/Renderer/Extension/Core.php	Emits mobile <source> elements when rendering images via Twig extension.
tests/fixtures/website/config.yml	Enables mobile variant settings in the integration test fixture site.
tests/IntegrationTests.php	Asserts generated HTML contains the expected mobile variant <source> and media query.