VSN-2720: Clean up vehicle planning toolbar, fix modal z-index and add date pill picker

Summary

Tightens the /dashboard/flottes/vehicule/planning page: kills leftover toolbar buttons, fixes a z-index bug where the date picker rendered under the intervention modal, and makes the date pill actually open a calendar.

Changes

• Toolbar cleanup
  • Remove "Calendrier" chip from the shared schedule toolbar (dead trigger on this view)
  • Remove the eye / eye-off toggle (driver-events filter) from the vehicle planning toolbar
• "Planifier une intervention" modal
  • Bump the shared date picker popover from z-[1500] → z-[10002] so it renders above the dialog (z-[10000])
  • Replace the native <select> for Fournisseur with the shadcn Select so it matches the rest of the app (purple hover, consistent styling, portal with correct z-index)
• Date pill
  • The Jeudi dd/mm/yyyy pill in the info bar is now a Popover trigger that opens a styled shadcn Calendar (same caption/dropdown layout as the modal date picker); picking a date updates the current view
• Timeline events
  • Remove the right-click context menu and its single "Copier" action on vehicle timeline slots; clean up the unused imports / state

Scope

• src/shared/components/schedule/schedule-toolbar.tsx
• src/shared/components/shadcn/form-field.tsx
• src/shared/sections/planning/planning-vehicle/add-intervention-dialog.tsx
• src/shared/sections/planning/planning-vehicle/draggable-time-slot.tsx
• src/shared/sections/planning/planning-vehicle/planning-view.tsx

Closes VSN-2720