Add a tiny glossary for loop, worker, gate, and preflight

[rxdt]

Goal

Add a small glossary so new contributors understand LoopGate terms quickly.

Suggested scope

Define:

• loop
• worker
• gate
• preflight

Acceptance criteria

• 4 short definitions.
• Plain English.
• Docs-only PR.

[Sajith-Santhosh]

Hi! I'd like to take a shot at this if it's still available. Thanks!

[rxdt]

Perfect! Thanks for taking this on.