task: #3625440 Back to DEV

Release plan: https://www.drupal.org/i/3625440

Back to DEV after the 1.0.4 release.

• composer.json version 1.0.4 to 1.0.x-dev.
• The fourteen drupal/varbase_*_base and drupal/vartheme_bs5_horizonaid constraints return to 1.0.x-dev, so the branch tracks the branch tips again. Same as the 1.0.3 Back to DEV.
• README badge back to 1.0.x-dev.

Tagged 1.0.4 at 6b378266. Tag pipeline 973894 green, 18/18 functional buckets.

AI-Generated: Yes

Checkpoints:

• File an issue
• Addition/Change/Update/Fix
• Testing to ensure no regression
• Automated unit testing coverage
• Automated functional testing coverage
• UX/UI designer responsibilities
• Readability
• Accessibility
• Performance
• Security
• Developer Documentation
• User Guide Documentation
• Reviewed by a human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Release notes snippet
• Release