feat: access labrinth backend (#6284)

* feat: redirect `/hosting` to archon

* feat: server invite notification type

* feat: direct email notification endpoint

* feat: revoke notification endpoint

* feat: specify users to remove notifications from

* refactor: insert notifications before sending emails

* refactor: rename endpoint

* refactor: remove archon redirect

* style: mark field unused

* feat: dedup external notifications

* feat: add server invite email templates

* style: remove unnecessary format

---------

Co-authored-by: sychic <47618543+Sychic@users.noreply.github.com>

apps/labrinth/migrations/20260525120000_server-invite-notification.sql

@@ -0,0 +1,28 @@
+INSERT INTO notifications_types
+	(name, delivery_priority, expose_in_user_preferences, expose_in_site_notifications)
+VALUES ('server_invite', 1, FALSE, TRUE);
+
+INSERT INTO users_notifications_preferences (user_id, channel, notification_type, enabled)
+VALUES (NULL, 'email', 'server_invite', FALSE);
+
+INSERT INTO notifications_templates
+	(channel, notification_type, subject_line, body_fetch_url, plaintext_fallback)
+VALUES
+	(
+		'email',
+		'server_invite',
+		'You''ve been invited to a server',
+		'https://modrinth.com/_internal/templates/email/server-invited',
+		CONCAT(
+			'Hi {user.name},',
+			CHR(10),
+			CHR(10),
+			'Modrinth user {inviter.name} has invited you to help manage {server.name} on Modrinth Hosting with the {server.role} role.',
+			CHR(10),
+			CHR(10),
+			'To accept or reject this invitation, open your Modrinth notifications: https://modrinth.com/dashboard/notifications',
+			CHR(10),
+			CHR(10),
+			'If you were not expecting this invitation, contact the server owner or reach out to Modrinth Support at https://support.modrinth.com'
+		)
+	);