Optimize CI Setup and Workflow

[Sendipad]

This PR optimizes the GitHub Actions CI workflow by introducing a dedicated setup script and removing extraneous dependencies.

Key improvements:

• Faster CI: By stripping out ERPNext and other large apps, we significantly reduce the time spent on bench get-app and bench setup requirements.
• Better Reliability: Manual database and user creation via MariaDB CLI avoids common permission issues often encountered with bench new-site in CI environments.
• Maintainability: The core setup logic is now encapsulated in a shell script, making the workflow YAML cleaner and the setup easier to test locally.
• Resource Efficiency: Disabling background workers (watch, schedule, etc.) and removing wkhtmltopdf reduces the CI footprint.

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PR created automatically by Jules for task 8369750222823590959 started by @Sendipad

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