Fix/doc updates

[Luchi5544]

closes #899
closes #902
closes #906
closes #907

Description

This PR resolves four documentation issues across the repository:

1. Root README Cleanup: Removed the leftover editor note ("i just need to create a draft pr") from the root README.md to ensure the header and Overview section read cleanly.
2. Package-Specific READMEs: Replaced the boilerplate Next.js README in the frontend package with FlowFi-specific content. Also added package-specific README.md files for the backend and contracts directories to orient new contributors.
3. CONTRIBUTING Guide Fixes: Fixed the malformed YAML front-matter wrapper in CONTRIBUTING.md so the main heading renders correctly, updated all flowfi/flowfi URLs to the correct LabsCrypt/flowfi repository, and corrected the PostgreSQL port documentation to 5433 (matching the docker-compose.yml mapping).
4. Authentication Documentation Link: Added a direct link to backend/docs/AUTHENTICATION.md in the root README.md's API Documentation section, and optionally cross-linked it from the Authentication Flow section in docs/ARCHITECTURE.md to ensure contributors have an entry point to the auth model.

Files Touched

• README.md
• frontend/README.md
• backend/README.md
• contracts/README.md
• CONTRIBUTING.md
• docs/ARCHITECTURE.md

Testing Instructions

• Verify that README.md and CONTRIBUTING.md render properly on GitHub without stray markdown characters.
• Ensure the links point to the correct LabsCrypt/flowfi repository and that the cross-links (e.g., to the Authentication Doc) resolve successfully.