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).

users.go

@@ -99,8 +99,8 @@ func (app *appContext) NewUserPostVerification(p NewUserParams) (out NewUserData
 		return
 	}
 	out.Created = true
-	// Invalidate Cache to be safe
-	app.jf.CacheExpiry = time.Now()
+	// Invalidate cache to be safe
+	app.InvalidateUserCaches()
 
 	app.storage.SetActivityKey(shortuuid.New(), Activity{
 		Type:       ActivityCreation,