build: create the initial application walking skeleton

[albertogalvez-dev]

Summary

This draft pull request implements Convive's initial executable walking skeleton.

It will validate the complete development path between the Angular frontend, Symfony backend, PostgreSQL database and Docker Compose environment.

Completed

• Bootstrap the Symfony 7.4 backend under apps/api.
• Select and validate PHP 8.5.
• Validate Composer configuration and platform requirements.
• Audit the initial backend dependencies.
• Establish the initial backend test directory.

Remaining work

• Bootstrap the Angular frontend.
• Create the Docker Compose development environment.
• Start PostgreSQL and configure Doctrine.
• Implement GET /api/v1/health.
• Configure the Angular development proxy.
• Render the API response in Angular.
• Add backend and frontend smoke tests.
• Add the initial continuous integration workflow.
• Document the startup and verification process.

Validation

• composer validate --strict
• composer check-platform-reqs
• composer audit --locked
• bin/console lint:yaml config
• bin/console about

Related issue

Closes #3