task: #3615661 Release Educare 1.0.0-alpha1

Closes #3615661.

Bumps drupal/educare to 1.0.0-alpha1 — the first release of the recipe:

• composer.json: version → 1.0.0-alpha1; tighten the 17 already-released drupal/varbase_*_base cross-dependencies and drupal/vartheme_bs5_educare from 1.0.x-dev to ~1.0.0. drupal/varbase_events_base and drupal/varbase_news_base stay 1.0.x-dev — neither has a tagged release yet.
• README.md: version badge → 1.0.0-alpha1.
• CHANGELOG.md: added (Keep a Changelog format).
• AGENTS.md: added.

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 human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Release notes snippet
• Release