Add "Date Created" and "Number of Days Open" to Suggestions Admin

[VirginiaWu11]

• Closes Add fields: "Date Created", "Number of Days Open" #2580

Summary

Adds two read-only fields to the Suggestions Administration table and details modal so admins can see when a correction/suggestion was submitted and how long it's been open.

• Date Created: the existing created_date, now exposed via the API (it was already in the DB but never selected for this view).
• Number of Days Open: computed client-side on load — today − createdDate for OPEN statuses (New, Pending), closedDate − createdDate for CLOSED statuses (Incorrect, Confirmed), frozen once closed.

Why server changes were needed

The ticket assumed this was front-end only, but two gaps required backend work:

• selectAll/selectById in suggestion-service.ts didn't select created_date for this view.
• There was no closed_date column, so the CLOSED-status interval couldn't be computed at all.

Changes

• Migration: new nullable closed_date timestamp column on suggestion.
• Server: selectAll/selectById now return created_date/closed_date; update stamps closed_date when status moves to Incorrect/Confirmed (idempotent — re-saving a closed record doesn't reset the timestamp) and clears it when moved back to New/Pending. Added the fields to Suggestion/SuggestionPostFields types and the PUT validation schema (POST schema explicitly excludes them — they're server-derived, not client-supplied).
• Client: added closedDate to the Suggestion and AdminSuggestion types; added a getDaysOpen/formatDate helper pair; inserted the two columns between Notes and Status in the table, and the two fields in the modal's Admin Notes section before Tipster details.

Notes

• Historically-closed rows have no closed_date and will show n/a for days-open until an admin re-saves them with a closed status (not backfilled — accepted tradeoff).
• Fixed a latent falsy-value bug in the shared DisplayText component's call site: a same-day suggestion has daysOpen === 0, which is falsy, so it's passed as a string to avoid being swallowed into "n/a".