Clarify archiving behavior for scheduled pipelines

What does this MR do and why?

Updates the Archive a project documentation to clarify what happens to scheduled CI/CD pipelines when a project is archived/unarchived.

Changes made

• Restructures the list items to use the "When you archive a project:" format.
• Updates unarchive section to clarify that scheduled pipelines resume automatically.
• Avoids duplication with the View inactive projects section by focusing on functional changes rather than UI behavior.
• Improves readability of the features list by using consistent plural forms.

Testing

I verified that "archived projects stop running scheduled CI/CD pipelines":

1. Created a test project with a scheduled pipeline set to run the next morning
2. Archived the project the evening before the scheduled run
3. Confirmed the scheduled pipeline did not execute at the scheduled time
4. Pipeline schedule remained visible in UI but was effectively inactive due to archived state
5. Last pipeline execution remained from before archiving

Result: Scheduled CI/CD pipelines do not run when a project is archived.

🔗 References

• Relates to Document whether archiving a project stops the ... (#25631)