v0.4.17 Add backend coverage baseline tooling

[roncodes]

Summary

• Adds backend coverage baseline scripts and Composer commands.
• Re-enables backend tests in server CI and uploads Clover coverage output.
• Corrects backend PHPUnit paths to use server source and test directories.

Validation

• Composer JSON and PHP syntax checks passed locally.
• Full Pest and coverage runs require installed Composer dependencies and coverage driver support.