Add started_at/ended_at datetime fields to Banner

[diti0-dot]

Closes #216

What is the goal of this PR and why is this important?

Adds support for scheduled banners with start/end dates

How did you approach the change?

Added started_at/ended_at datetime fields to Banner, created an :active scope to filter by current date, and updated display_banner helper to show all active banners instead of just the last one.

UI Testing Checklist

Anything else to add?

Should I also add the started_at and ended_at fields to the banners/new form?

[maebeale]

@diti0-dot would you rebase main into this branch, re-run tests locally and push updates so conflicts are removed and it can pass ci?

[maebeale]

Closing in favor of a new PR from origin — the fork's branch had unresolvable stale merge refs.

[maebeale]

Hey @diti0-dot! CI is failing because db/schema.rb on your fork's banner branch has merge conflict markers (the <<<<<<<, =======, >>>>>>> lines) that were committed during a previous rebase. Since the PR comes from your fork, we can't push fixes directly.

Here's how to fix it from your local clone:

# 1. Make sure you're on the banner branch
git checkout banner

# 2. Fetch the latest upstream main
git fetch upstream main

# 3. Reset your branch to upstream main
git reset --hard upstream/main

# 4. Cherry-pick the clean commit we prepared (from the origin repo)
git cherry-pick c6042ed28

# 5. Force push to your fork
git push origin banner --force

If you don't have upstream set up yet:

git remote add upstream https://github.com/rubyforgood/awbw.git

The key issue is that db/schema.rb had conflict markers from a rebase that weren't fully resolved. The cherry-pick above has a clean version with only the banner started_at/ended_at changes.

[diti0-dot]

@maebeale Thanks for guiding me through this 🫶. I really appreciate the help. Please let me know if anything else needs to be updated!