v1.21.0

🐛 Bug Fixes

• Blocks: fix str_starts_with() type error when image is an array from Filament FileUpload in hero and contact_form blocks
• Blocks: fix hero "Top (Behind Text)" image position — image now renders as full-bleed background behind text with WCAG gradient overlay
• CMS: Content Blocks section is now expanded by default when editing a page translation
• CMS: blocks are now collapsed by default to make navigation easier
• CMS: block types are now sorted alphabetically in the add-block picker

🧪 Tests

• Blocks: add tests for hero block array image handling, top position rendering, and contact_form array image handling
• CMS: add tests for collapsed-by-default and alphabetical sort of blocks

📝 Documentation

• AGENTS.md: strengthen TDD requirement with explicit RED/GREEN phases, anti-false-positive gate, regression test commitment, and commit body conventions
• Skills: update issue-to-mr with step-by-step TDD (RED → GREEN), naming conventions, and anti-regression gate; update git-changelog-workflow and branch-and-commits.md with required Regression test: / Feature test: body in commit messages