Add DAG run missed-deadline metadata to Grid API

[imrichardwu]

This PR introduces backend and API support for exposing per-DAG-run deadline information to the UI.

Changes included

API and data model

• GridRunsResponse gains a has_missed_deadline: bool field, allowing the Grid view to surface
  deadline status without additional API calls.

New private UI endpoint

• Adds a private UI router mounted at /ui/deadlines/{dag_id}/{run_id}.
• The endpoint fetches all Deadline rows for the given DAG run, joined with their associated
  DeadlineAlert records.
• Results are ordered by deadline_time and returned as DeadlineResponse objects.

New response model

DeadlineResponse includes:

• id
• deadline_time
• missed
• created_at
• alert_name (nullable)
• alert_description (nullable)

OpenAPI

• Updates _private_ui.yaml to document the new endpoint and response schema.
• Regenerates the TypeScript client accordingly.

Notes

• No UI rendering logic is included in this PR.
• This PR only exposes the data required by the UI, keeping frontend concerns separate.

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[ferruzzi]

The yaml and python portions look like they are following the patterns of the surrounding code. The typescript portion is absolute witchcraft but I think it looks right compared the surrounding code for other features.

Approving with the caveat that someone with more front-end experience needs to also approve it, and assuming the CI goes green

[pierrejeambrun]

I'll open a follow up PR to fix some issues here. (General design, pagination is missing, ordering options, payload format etc....)

Please if you have any doubt wait for additional reviews before merging.