errors: report EVERY server/gateway error to GitHub Issues

PHP api/index.php:
- DB connection failure (500) now calls _phpErrorReport()
- Main router catch-all (500) now calls _phpErrorReport()
- undoTransaction DB error (500) now calls _phpErrorReport()

PHP api/cron_smart_shopping.php:
- cron Throwable catch now calls _phpErrorReport() before exit(1)
  (fires even in CRON_MODE since _phpErrorReport() has its own guard)

Scale Gateway GatewayWebSocketServer.kt:
- onError() now calls ErrorReporter.report(ex, ...) in addition to Log.e

Combined with previous kiosk commit, every error path in the entire
EverShelf stack now sends an automatic GitHub Issue.

api/index.php

@@ -188,6 +188,7 @@ try {
 } catch (Exception $e) {
     http_response_code(500);
     echo json_encode(['error' => 'Database connection failed: ' . $e->getMessage()]);
+    _phpErrorReport($e->getMessage(), $e->getFile(), $e->getLine(), $e->getTraceAsString(), get_class($e));
     exit;
 }
 
@@ -432,6 +433,7 @@ try {
 } catch (Exception $e) {
     http_response_code(500);
     echo json_encode(['error' => $e->getMessage()]);
+    _phpErrorReport($e->getMessage(), $e->getFile(), $e->getLine(), $e->getTraceAsString(), get_class($e));
 }
 endif; // end !CRON_MODE
 
@@ -1652,6 +1654,7 @@ function undoTransaction(PDO $db): void {
         $db->rollBack();
         http_response_code(500);
         echo json_encode(['error' => 'DB error: ' . $e->getMessage()]);
+        _phpErrorReport($e->getMessage(), $e->getFile(), $e->getLine(), $e->getTraceAsString(), get_class($e));
     }
 }