Add GitHub templates and CI workflow

- PR template
- Issue templates (bug report, feature request)
- Hassfest validation workflow

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,20 @@
+## Description
+
+Brief description of the changes.
+
+## Type of Change
+
+- [ ] Bug fix
+- [ ] New feature
+- [ ] Documentation update
+- [ ] Other (describe):
+
+## Testing
+
+Describe how you tested these changes.
+
+## Checklist
+
+- [ ] Code follows project style guidelines
+- [ ] Changes have been tested locally
+- [ ] Documentation updated (if applicable)