feat: add minute randomization option for post scheduling

[rubymignot]

What kind of change does this PR introduce?

Feature: Add “Randomize minute” scheduling option (default ON), update CreatePostDto, and wire backend + frontend to support random minute within the selected hour.

Why was this change needed?

• Smoother posting cadence.
• Gives explicit user control to disable randomization when precise minute is needed.
• Keeps system consistent by persisting the final publishDate and using it for queue delays.

Key points:

• Frontend:
  • ManageModal: add “Randomize minute” checkbox (default ON).
  • UX:
    • Unchecking immediately clamps the picker to :00 (visible to user).
    • Rechecking re-randomizes to a different minute.
    • Not showing modal if we're editing.

Other information

• This is backward compatible for scheduled posting and cron/worker flows (they already rely on publishDate).
• This is related to Randomize minute within scheduled hour #985
• This is also my first contribution to open-source!!! Please be nice lol

Checklist

• I have read the CONTRIBUTING guide.
• I checked that there were not similar issues or PRs already open for this.
• This PR fixes just ONE issue (adds random-minute scheduling with a UI toggle, plus DTO).

[vercel]

@rubymignot is attempting to deploy a commit to the Listinai Team on Vercel.

A member of the Team first needs to authorize it.

[egelhaus]

@sentry review

[seer-by-sentry]

⚠️ We couldn't complete your request
Prevent AI only supports U.S. data storage at this time.
📘 Learn more about Prevent AI