Purpose:
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- It should be easier to visualize maintenance requests than what is possible today. The calendar view is useful but does not provide a comprehensive overview of all equipment or work centers, nor the ability to plan interventions easily.
- It should be much easier to perform maintenance directly from an equipment or work center, instead of creating a maintenance request manually.
- It should also be easy to quickly visualize which equipment is currently undergoing maintenance and update their status once the maintenance is completed.

With this commit:
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- Makes maintenance planning more easier to manage by adding gantt view by equipment/workcenter.
- Replaced the `Maintenance Calendar` menu with `Planning by Equipment` and `Planning by Workcenter`, providing a more practical way to plan maintenance requests by resources rather than relying on the calendar view.
- Allows creating maintenance requests directly from equipment or work center views, reducing manual effort.
- Prevents scheduling conflicts by showing unavailable workcenter intervals due to workorders or non-working hours.
- Removes the `Request Date` field from maintenance requests as it is redundant with `Scheduled Date`; `Scheduled Date` more accurately reflects the intended start of the maintenance request, whereas `Request Date` only indicates when the request was created.
- The Gantt view defaults to filtering records for the respective workcenter/equipment by `Todo` and `Active`, excluding `Done` and `Archived` maintenance requests, to focus on the remaining active requests.
- It also makes other views (e.g., Kanban, List, Pivot, etc.) of Maintenance Requests available alongside the Gantt view
under `Planning by Equipment` or `Planning by Workcenter`, with the default grouping by equipment or workcenter respectively.
- Improve planning by adding a Plan Popup for unscheduled maintenance requests. It is especially useful when maintenance planners have created requests but are not yet sure when they should be scheduled.
- The Plan Popup applies default `Todo` and `Active` filters to prevent accidental planning of cancelled or already repaired requests.

task-4698325