docs: align the README with the current product

[OthmaneZ05]

Summary of Changes

Rewrites the README so it describes what Torollo actually ships today. The hook now leads with the product's core loop — guided roadmaps auto-graded against the real state of your local containers — instead of a generic sandbox pitch.

• New top section pitching the validation loop ("you can't bluff it"), with a placeholder comment reserved for a future demo GIF above the screenshot.
• New "Guided, auto-graded roadmaps" section: what validators check, the current EN/FR catalogue (resilient three-tier, cache-aside Redis, Redis queue workers) with difficulty/duration taken from the roadmap files, and pointers to the open format docs.
• Quick Start now routes the reader to their first roadmap instead of stopping at npx torollo start.
• Removed the "Coming Very Soon" section and its stale promises (Terraform/IaC generation, Kafka). IaC export is now mentioned only as a community idea in Contributing.
• Node list updated to include the RabbitMQ broker node (with management console) and reorganized; traffic simulator/terminals/port shortcuts summarized under it.
• Self-Hosting & Network Exposure section kept as-is; Contributing section added; Philosophy tightened (local-first, MIT core).

Types of Changes

• New feature / node type addition
• Bug fix (non-breaking change resolving an issue)
• Refactoring / structural cleanup
• Documentation update

Verification & Testing

Automated Checks

• Run npm run lint successfully with no errors
• Run npm run build successfully with no compilation errors
• Run npm test successfully (all tests pass)

Manual Verification

Docs-only change; backend (lint, build, jest) and frontend (lint, build, vitest — 231 tests) all pass. Every factual claim was cross-checked against the repo: roadmap titles, difficulties, durations and step counts against the JSON files in roadmaps/; the "what validators check" list against the step validators; the RabbitMQ management-console claim against the image tag (rabbitmq:3-management-alpine) and its published port; the anchor link into docs/adding-a-node.md and all relative links resolved. Grepped the final README to confirm zero mentions of retired promises or pricing.

Checklist

• My code follows the repository's code style and lint standards
• I have updated the documentation or instructions if necessary
• All unit and integration tests are passing