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>

tests/Http/ErrorLoggerTest.php

@@ -0,0 +1,95 @@
+<?php
+
+namespace MintyPHP\Tests\Http;
+
+use MintyPHP\Http\ErrorLogger;
+use PHPUnit\Framework\TestCase;
+
+class ErrorLoggerTest extends TestCase
+{
+    private string $logFile;
+
+    protected function setUp(): void
+    {
+        $this->logFile = 'storage/logs/errors/error-' . date('Y-m-d') . '.log';
+        // Remove the file so each test starts clean.
+        if (is_file($this->logFile)) {
+            @unlink($this->logFile);
+        }
+    }
+
+    public function testLogWritesJsonLineEntry(): void
+    {
+        $exception = new \RuntimeException('Test error', 42);
+        $data = [
+            'exception' => [
+                'class' => 'RuntimeException',
+                'message' => 'Test error',
+                'code' => 42,
+                'file' => '/app/web/index.php',
+                'line' => 10,
+                'trace' => [
+                    ['file' => '/app/web/index.php', 'line' => 10],
+                ],
+            ],
+            'request' => [
+                'request_id' => 'abc-123',
+                'channel' => 'web',
+                'method' => 'GET',
+                'url' => '/admin/dashboard',
+                'ip' => '127.0.0.1',
+                'user_id' => 5,
+                'tenant_id' => 1,
+            ],
+            'environment' => [
+                'php_version' => '8.5.0',
+                'memory_peak' => 12 * 1024 * 1024,
+            ],
+            'queries' => [],
+        ];
+
+        ErrorLogger::log($exception, $data);
+
+        $this->assertFileExists($this->logFile);
+
+        $lines = array_filter(explode("\n", (string) file_get_contents($this->logFile)));
+        $this->assertCount(1, $lines);
+
+        $entry = json_decode($lines[0], true);
+        $this->assertIsArray($entry);
+        $this->assertSame('error', $entry['level']);
+        $this->assertSame('abc-123', $entry['request_id']);
+        $this->assertSame('RuntimeException', $entry['exception']['class']);
+        $this->assertSame('Test error', $entry['exception']['message']);
+        $this->assertArrayHasKey('ip_hash', $entry['request']);
+        $this->assertStringStartsWith('sha256:', $entry['request']['ip_hash']);
+        // Raw IP should NOT be in the log.
+        $this->assertStringNotContainsString('127.0.0.1', json_encode($entry));
+    }
+
+    public function testLogRedactsIpAddress(): void
+    {
+        $exception = new \RuntimeException('IP test');
+        $data = [
+            'request' => ['ip' => '192.168.1.42', 'request_id' => 'test-id'],
+            'exception' => [],
+            'environment' => [],
+        ];
+
+        ErrorLogger::log($exception, $data);
+
+        $this->assertFileExists($this->logFile);
+        $contents = (string) file_get_contents($this->logFile);
+        $this->assertStringNotContainsString('192.168.1.42', $contents);
+        $this->assertStringContainsString('sha256:', $contents);
+    }
+
+    public function testLogNeverThrowsOnFailure(): void
+    {
+        // Even with broken data, log() must not throw.
+        $exception = new \RuntimeException('safe test');
+        ErrorLogger::log($exception, []);
+
+        $this->assertTrue(true); // If we get here, no exception was thrown.
+    }
+}