Calendar view rework

### Description

The issue is for covering the work of changing the design of the calendar view.

We will start with a static mockup to get feedback from the community and then move on with the implementation.

These are the current pages

### Use case/motivation

The current calendar view isn't intuitive and easy to get a lot of info especially when you have multiple mixed runs spreading across different days and hours. Additionally, there is no distinction for backfill runs.

### Related issues

_No response_

### Are you willing to submit a PR?

- [x] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

Start with the current calendar pages shown in the issue and compare them with the proposed static mockup. Clarify the intended layout, treatment of mixed runs across days and hours, and backfill distinction with maintainers before locating implementation entry points. Done is a reviewed mockup with an agreed implementation scope.

Written by the indexing model from the issue text.