accounts: invalidate web user cache on changes as well

previously used app.jf.CacheExpiry = time.Now(), now either call
app.InvalidateJellyfinCache() (when we only need it to get a user),
or app.InvalidateUserCaches() (when the web user list needs to be
updated).

user-d.go

@@ -104,7 +104,7 @@ func (app *appContext) checkUsers() {
 			expiry.DeleteAfterPeriod = true
 			app.storage.SetUserExpiryKey(user.ID, expiry)
 		}
-		app.jf.CacheExpiry = time.Now()
+		app.InvalidateJellyfinCache()
 		if contact {
 			if !ok {
 				continue