Prepare php-transformer wave 3 release fixes

[chubes4]

Summary

• integrate wave-3 php-transformer fixes for editor-valid image/SVG output and runtime-island classification
• reduce div/section/button fallback behavior with additional parity fixtures
• update php-transformer lockfile dependency symfony/deprecation-contracts from v3.7.0 to v3.7.1

Verification

• composer validate --strict in php-transformer passed
• composer outdated --direct --strict in php-transformer reported direct dependencies current
• composer outdated --strict in php-transformer reported dependencies current after lockfile update
• composer test in php-transformer passed, including runtime contracts, unit tests, 212 parity fixtures, and package install proof
• npm ci in php-transformer/tools/visual-parity
• npm test in php-transformer/tools/visual-parity passed

Release notes

• Current php-transformer version remains 0.2.4; recommended next release is likely 0.2.5 after this lands.
• Do not hand-edit CHANGELOG.md; use Homeboy release flow from the accepted merged commit.
• Unrelated generated figma-transformer/vendor/composer/installed.php is dirty in the local worktree and intentionally excluded from this PR.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode with openai/gpt-5.5
• Used for: Drafting and verifying the php-transformer wave-3/release-prep changes with Chris reviewing and directing the work.