fix(events): audit pass — 7 correctness fixes across the events system

Backend:
- tools.py: apply UTC normalization to update_event datetime fields
  (matched create_event which already did this)
- events.py service: allow end_dt/recurrence/project_id to be cleared
  via update_event by permitting None for nullable fields
- events.py service: find_events_by_query now returns upcoming events
  first, falling back to past — prevents AI tools from mutating stale
  past events when a future match exists
- events.py service: list_events now uses overlap logic (start <= to
  AND end >= from) so multi-day events spanning the query boundary
  are included; previously only start_dt was checked

Frontend:
- ToolCallCard: fire fable:calendar-changed on created/updated/deleted
  so CalendarView refetches without requiring a manual page refresh
- KnowledgeView: replace raw apiGet('/api/events') with listEvents()
  client function; also fix today bar which was reading .events off a
  flat array (always empty) — now correctly receives EventEntry[]
- HomeView: use full ISO strings for event date range instead of naive
  UTC-midnight strings; deduplicate inline date math via _dateRange()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/ToolCallCard.vue

@@ -270,8 +270,11 @@ async function openEventSlideOver(id: number | undefined) {
   }
 }
 
-function closeEventSlideOver() {
+function closeEventSlideOver(changed = false) {
   eventSlideOverOpen.value = false;
+  if (changed) {
+    document.dispatchEvent(new Event("fable:calendar-changed"));
+  }
 }
 </script>
 
@@ -522,9 +525,9 @@ function closeEventSlideOver() {
     :event="eventSlideOverEntry"
     initial-date=""
     @close="closeEventSlideOver"
-    @created="closeEventSlideOver"
-    @updated="closeEventSlideOver"
-    @deleted="closeEventSlideOver"
+    @created="() => closeEventSlideOver(true)"
+    @updated="() => closeEventSlideOver(true)"
+    @deleted="() => closeEventSlideOver(true)"
   />
 </template>