SaaS block library + `npx` scaffold for cursor rules

## Feature Request: SaaS block library + `npx` scaffold for cursor rules

SaaS apps are everywhere, yet there’s no design system truly built around their real-world block needs. We need:
- **Hundreds of SaaS-specific blocks** (chat inbox, timeline, multitenant signup, notification center, role management, etc.)
- Ready for mono/multitenant use cases
- Fully responsive, accessible, and **deeply Mantine in spirit** — not another remix of Spectrum or ShadCN

**Additionally**, propose a CLI `npx create-mantine-cursor` that scaffolds:
- TypeScript + React + Mantine layout
- A `cursor-rules.mdc` file with customizable LLM-ready coding rules
- Preloaded setup for accessibility-first + perf-aware projects

This initiative would massively reduce bootstrapping time and encode Mantine’s best practices into every keystroke.

No files or tests are identified. Start by scoping the SaaS block library separately from the `npx create-mantine-cursor` scaffold, then define the supported blocks, generated TypeScript/React/Mantine project structure, cursor-rules.mdc contents, and acceptance checks for responsiveness, accessibility, and performance.

Written by the indexing model from the issue text.