Add comprehensive quality tooling and fix code style issues

Quality Tools Added:
- PHPStan (Level 8) for static analysis
- PHP_CodeSniffer (PSR-12) for code style
- Updated PHPUnit test suite with type safety

Code Improvements:
- Fixed all PHPStan Level 8 errors (13 issues)
- Auto-fixed 25 PSR-12 code style violations
- Added proper type hints for arrays and method parameters
- Fixed PDOStatement|false handling in api.php and tests
- Improved null-safety for parse_url() calls

Configuration:
- phpstan.neon: Level 8, analyzes src/ and tests/
- phpcs.xml: PSR-12 standard, excludes vendor/
- docker-compose.yml: Mount config files for tooling
- composer.json: Add phpstan, phpcs, phpcbf scripts

Documentation:
- Updated README.md with testing and quality sections
- Updated AGENTS.md with quality gates and workflows
- Added pre-commit checklist for developers

All tests pass (9/9), PHPStan clean (0 errors), PHPCS compliant (1 warning)

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

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

tests/Integration/CrawlerIntegrationTest.php

@@ -18,7 +18,8 @@ class CrawlerIntegrationTest extends TestCase
         // Create a test job
         $stmt = $this->db->prepare("INSERT INTO crawl_jobs (domain, status) VALUES (?, 'pending')");
         $stmt->execute(['https://httpbin.org']);
-        $this->testJobId = $this->db->lastInsertId();
+        $lastId = $this->db->lastInsertId();
+        $this->testJobId = is_numeric($lastId) ? (int)$lastId : 0;
     }
 
     protected function tearDown(): void

tests/Unit/CrawlerTest.php

@@ -17,7 +17,8 @@ class CrawlerTest extends TestCase
         // Create a test job
         $stmt = $db->prepare("INSERT INTO crawl_jobs (domain, status) VALUES (?, 'pending')");
         $stmt->execute(['https://example.com']);
-        $this->testJobId = $db->lastInsertId();
+        $lastId = $db->lastInsertId();
+        $this->testJobId = is_numeric($lastId) ? (int)$lastId : 0;
     }
 
     protected function tearDown(): void

tests/Unit/DatabaseTest.php

@@ -42,6 +42,7 @@ class DatabaseTest extends TestCase
     {
         $db = Database::getInstance();
         $stmt = $db->query('SELECT 1 as test');
+        $this->assertNotFalse($stmt, 'Query failed');
         $result = $stmt->fetch();
 
         $this->assertEquals(['test' => 1], $result);