Replace the previous dual-parameter approach (app_type/app/appType) with a single required `app: String` parameter across all Tauri commands. This change:
- Introduces unified `parse_app()` helper replacing complex `resolve_app_type()` logic
- Updates all backend commands in config, mcp, and provider modules
- Aligns frontend API calls to use consistent `app` parameter naming
- Simplifies MSW test handlers by removing optional parameter handling
This improves API clarity and reduces parameter ambiguity while maintaining backward compatibility through error handling.
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