Add date and value filters to Backfills UI API

[Phinhas214]

Related: #53049

Add date and value filters to the Backfills tab UI.

Adds 6 of the 8 filters requested in #53049 to the Backfills tab: start_date, end_date,
created_at, completed_at, reprocess_behavior, and max_active_runs.
The remaining 2 filters duration and status are deliberately left out see "Open questions for reviewers" below.

Before

After

backfill_filters_recording.mov

Open questions for reviewers

duration

• Motivation:Surfaces long-running backfills that may impact system performance
• Backfill has no duration column. DagRun derives its duration from
  end_date - start_date via a dialect-aware hybrid_property, but Backfill has neither of
  those columns. The closest fields are created_at/completed_at. Mirroring DagRun's pattern directly on those fields means a running
  backfill has completed_at = NULL, so duration IS NULL, and NULL fails any SQL
  comparison. This implementation would silently exclude every
  currently running backfill, even though "surface long-running backfills" (the motivation for duration filter) should include ones still running in my opinon.
• One option: compute duration as
  now() - created_at when completed_at IS NULL, so in-progress backfills still get a
  duration value. Would you like me to implement it that way, or handle it differently?

status

• Motivation:Surface failed or incomplete backfills
• similarly, Backfill has no status column — only is_paused and
  completed_at. list_backfills_ui already has a partial precedent (active, based on
  completed_at IS NULL) but this definition of status would only give us running vs. finished states.
• Should status build on that directly, or does it need to look at
  associated DagRun states (e.g: join out to child DagRun states to support "failed" state?)

Happy to follow up on duration/status once there's a direction.

---

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Generated-by: Claude Code (Sonnet 5) following the guidelines

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[bbovenzi]

Please spend some time cleaning up the code. There are some pretty clear mistakes here.

Let's rebase once #70159 is merged

[Phinhas214]

Please spend some time cleaning up the code. There are some pretty clear mistakes here.

Let's rebase once #70159 is merged

Thank you @bbovenzi for the review. I fixed up the issues you surfaced and rebased my changes after #70159.

Let me know that how you think I should tackle duration and status filters and I'll be glad to work on it in a separate PR.

[bbovenzi]

Something broke with your rebase. Closing this. Feel free to open up a new PR with only changes to the backfill filters.