feat: add developer error page with request ID tracking and structured logging

Custom-built error handler for the web channel that shows a tabbed debug
dashboard (exception, request context, environment, SQL queries) in dev mode
and a clean branded error page with copyable request ID in prod mode.
All errors are logged as JSON lines to storage/logs/errors/ for lookup by
request ID. Uses the project's design tokens for visual consistency.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/index.php

@@ -26,6 +26,7 @@ chdir(__DIR__ . '/..');
 require 'vendor/autoload.php';
 require 'config/config.php';
 require 'lib/Support/helpers.php';
+\MintyPHP\Http\ErrorHandler::register();
 $container = require 'lib/App/registerContainer.php';
 setAppContainer($container);