Replace placeholder README with a complete Coxyz organization profile (FR)

[Copilot]

The repository README was a placeholder and did not describe the Coxyz organization. This change replaces it with a structured French profile covering mission, activities, repository scope, and operating principles.

• Content overhaul

  • Replaced the one-line placeholder with a full organization-facing README.
  • Added clear sections: identity, mission, what Coxyz builds, and GitHub organization contents.

• Operational scope documented

  • Described core workstreams: web/apps, backend APIs, workflow automation, software quality, and technical documentation.

• Working model clarified

  • Added concise principles (quality, security, collaboration, impact) plus issue-based contact guidance.

Example of the new README structure:

## Ce que fait Coxyz
- développement d’applications web et d’outils métiers
- conception de services backend et d’API
- automatisation de workflows
- amélioration continue (tests, CI/CD, sécurité)

Original prompt

Fait un readme qui va decrire tous ce que fait mon organisation Coxyz