feat(commands): add handoffs support for speckit compatibility (#410)

* feat(commands): add handoffs support for speckit compatibility

- Upgrade frontmatter parser to use js-yaml for complex YAML support
- Add HandoffDefinition interface for speckit-style workflow transitions
- Update CommandFrontmatter and CommandDefinition to include handoffs
- Add comprehensive tests for backward compatibility and complex YAML
- Fix type parameters in auto-slash-command and slashcommand tools

Closes #407

* fix(frontmatter): use JSON_SCHEMA for security and add extra fields tolerance tests

- Use JSON_SCHEMA in yaml.load() to prevent code execution via YAML tags
- Add tests to verify extra fields in frontmatter don't cause failures
- Address Greptile security review comment

---------

Co-authored-by: sisyphus-dev-ai <sisyphus-dev-ai@users.noreply.github.com>

src/features/claude-code-command-loader/loader.ts

@@ -78,6 +78,7 @@ $ARGUMENTS
         model: sanitizeModelField(data.model, isOpencodeSource ? "opencode" : "claude-code"),
         subtask: data.subtask,
         argumentHint: data["argument-hint"],
+        handoffs: data.handoffs,
       }
 
       commands.push({