fix: pass auth to get_events in post_slack endpoint

post_slack called get_events without forwarding the auth parameter,
causing check_auth inside get_events to receive a raw Depends()
descriptor instead of the authenticated User, resulting in 401.

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

Author: pythoninthegrass

app/main.py

@@ -465,7 +465,7 @@ def post_slack(
 
     check_auth(auth)
 
-    get_events(location=location, exclusions=exclusions)
+    get_events(auth=auth, location=location, exclusions=exclusions)
 
     # open json file and convert to list of strings
     msg = fmt_json(json_fn)