Huge refactor for backend and client

This is barely functionnal, but at least it can display some data without crashing
Most other functionnalities other than displaying events are broken, and so are the relative date operations, they need to be fixed asap

components/calendar/state/monthly/DayTile.vue

@@ -1,5 +1,5 @@
 <script lang="ts" setup>
-import { areDatesIdentical, type LeimDate } from '@/models/Date'
+import { areDatesIdentical, type RPGDate } from '@/models/Date'
 import { useCalendar } from '@/stores/CalendarStore'
 import { useCalendarEvents } from '@/stores/EventStore'
 import { useElementBounding } from '@vueuse/core'
@@ -7,10 +7,10 @@ import { storeToRefs } from 'pinia'
 import { computed, ref, type ComputedRef } from 'vue'
 
 import CalendarEventButton from '../../CalendarEvent.vue'
-import type { CalendarEvent } from '@/models/Events'
+import type { CalendarEvent } from '~/models/CalendarEvent'
 
 const props = defineProps<{
-  date: LeimDate
+  date: RPGDate
   faded?: boolean
 }>()