[schedule] Fix bugs in the schedule consumer pages

[frankrousseau]

Problem

• Fallback end dates added estimation (minutes) as days: bars hundreds of days long on entity and person pages
• Sequence, episode and edit pages let users drag bars but never saved the change; the person page wired save handlers on bars that were never editable; entity pages were editable by everyone, including artists
• The team schedule crashed on an unknown production id in the URL and the main schedule date filters did nothing
• Task type page: the date clamp read never-assigned state, the socket refresh condition could never be true, before/after ghosts mutated tasks in the Vuex store, and the date watchers crashed when no schedule item was found
• Load and save failures were silent (stuck spinners, error flags never raised) and afterDestroy is not a Vue hook, so person tasks were never cleaned from the store
• A deleted task type crashed item building; days off and timesheets were refetched on every socket event or bar drag

Solution

• Convert estimations with minutesToDays before computing fallback end dates (mixin, composable, person page)
• Wire saveTaskScheduleItem on sequence/episode/edit and gate editable on manager or department supervisor on the person and entity pages
• Guard the team schedule production filter, apply the main schedule date fields to the timeline and clamp task type bars to the production range
• Fix the nbSelectedTasks check, copy ghost tasks before mutating them, guard the task type date watchers and skip items whose task type is gone
• Add catches, error flags and spinner cleanup on the load/save paths; rename afterDestroy to unmounted
• Cache the days off fetch per date range, index tasks by id when attaching timesheets, drop the studio-wide days off refetch after drags