Implements template validation for bd lint and bd create --validate: - ValidateTemplate() checks description for required sections - LintIssue() validates an existing issue - TemplateError provides actionable missing section details - Case-insensitive, flexible heading matching Also fixes: close.go missing session parameter in CloseIssue calls 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>