[DevOps] CI: cache dependencies and parallelize frontend/backend jobs

[JayWebtech]

Overview

Faster PR feedback loops.

Technical Requirements

• npm cache in GitHub Actions.
• Matrix or parallel jobs where independent.
• Document expected CI time budget.

[caramel222]

@caramel222 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

hi, can i work on this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @caramel222 to this issue.

[GideonBature]

@GideonBature has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Greetings Maintainer,

Please I will love to work on this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @GideonBature to this issue.