fix(fusion_schedule): stop archiving valid events on @removed=changed

Microsoft Graph's delta API returns @removed={reason:'changed'} when an
event drifts outside the original delta-query window — the event still
exists upstream. The old code treated any truthy @removed the same as a
real delete and archived the local calendar.event. Combined with
_find_existing_event filtering by active=True, every subsequent sync
recreated a duplicate (then archived it on the next pass), accumulating
5x duplicates and emptying the user's calendar.

- _process_microsoft_event: only archive on isCancelled or
  @removed.reason='deleted'; skip on @removed.reason='changed'
- _process_microsoft_event link path: reactivate when MS Graph confirms
  a previously-archived event still exists
- _process_microsoft_event iCalUId path: same reactivation
- _find_existing_event: include archived records so wrongly-archived
  duplicates are reused instead of piling up
- callers reactivate the matched archived record

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_schedule/__manifest__.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 {
     'name': 'Fusion Schedule',
-    'version': '19.0.2.0.0',
+    'version': '19.0.2.1.0',
     'category': 'Services/Appointment',
     'summary': 'Multi-calendar sync, portal booking, and shareable scheduling links',
     'description': """