fix(astrolabe): Fix revoke access button HTTP method mismatch

The "Revoke Access" button in Astrolabe personal settings was failing
with "Unable to connect to server" error in multi-user basic auth mode.

Root cause: The JavaScript sends a POST request but the route was
configured to accept DELETE. Changed the route to:
- Use POST method (matching the JavaScript fetch call)
- Use /api/v1/background-sync/credentials/revoke path (avoiding
  conflict with storeAppPassword which uses POST on the base URL)

Added integration test that verifies the complete revoke flow:
enable background sync → click revoke → verify credentials deleted.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

third_party/astrolabe/appinfo/routes.php

@@ -47,8 +47,8 @@ return [
 		],
 		[
 			'name' => 'credentials#deleteCredentials',
-			'url' => '/api/v1/background-sync/credentials',
-			'verb' => 'DELETE',
+			'url' => '/api/v1/background-sync/credentials/revoke',
+			'verb' => 'POST',
 		],
 		[
 			'name' => 'credentials#getStatus',