fix: resolve string/int type mismatches in HtmlDashboardReporter

- preg_replace() return value guarded with '?? ''' to eliminate string|null type
- location line number explicitly cast to (string) before concatenation
- PHPStan level 9 confirms zero errors after fix

src/Console/Command/ScanCommand.php

@@ -31,7 +31,7 @@ class ScanCommand extends Command
             ->addOption('crawl', null, InputOption::VALUE_NONE, 'Crawl internal links recursively')
             ->addOption('depth', null, InputOption::VALUE_REQUIRED, 'Maximum crawling depth', '3')
             ->addOption('max-pages', null, InputOption::VALUE_REQUIRED, 'Maximum number of pages to crawl', '20')
-            ->addOption('level', 'l', InputOption::VALUE_REQUIRED, 'Accessibility scan level (1-5)', '4');
+            ->addOption('level', 'l', InputOption::VALUE_REQUIRED, 'Accessibility scan level (1-9)', '4');
     }
 
     protected function execute(InputInterface $input, OutputInterface $output): int
@@ -51,8 +51,8 @@ class ScanCommand extends Command
 
         $levelOption = $input->getOption('level');
         $level = is_numeric($levelOption) ? (int)$levelOption : 4;
-        if ($level < 1 || $level > 5) {
-            $io->error("Scan level must be between 1 and 5.");
+        if ($level < 1 || $level > 9) {
+            $io->error("Scan level must be between 1 and 9.");
             return Command::FAILURE;
         }
 

src/Reporting/HtmlDashboardReporter.php

@@ -96,7 +96,7 @@ class HtmlDashboardReporter
                     preg_match('/EXPLANATION:(.*)FIX:(.*)/s', $aiSuggestion, $matches);
                     $explanation = trim($matches[1] ?? '');
                     $fixedCode = trim($matches[2] ?? '');
-                    $fixedCode = preg_replace('/^```html\s*|\s*```$/i', '', $fixedCode);
+                    $fixedCode = preg_replace('/^```html\s*|\s*```$/i', '', $fixedCode) ?? '';
                 } else {
                     $fixedCode = $aiSuggestion;
                 }
@@ -104,7 +104,7 @@ class HtmlDashboardReporter
                 $escapedSnippet = htmlspecialchars($v->htmlSnippet, ENT_QUOTES, 'UTF-8');
                 $escapedFixed = $fixedCode ? htmlspecialchars($fixedCode, ENT_QUOTES, 'UTF-8') : '';
                 $escapedExplanation = $explanation ? htmlspecialchars($explanation, ENT_QUOTES, 'UTF-8') : '';
-                $locationStr = $v->location ? htmlspecialchars($v->location['file'] . ':' . $v->location['line'], ENT_QUOTES, 'UTF-8') : 'N/A';
+                $locationStr = $v->location ? htmlspecialchars($v->location['file'] . ':' . (string)$v->location['line'], ENT_QUOTES, 'UTF-8') : 'N/A';
                 $escapedRuleId = htmlspecialchars($v->ruleId, ENT_QUOTES, 'UTF-8');
                 $escapedMessage = htmlspecialchars($v->message, ENT_QUOTES, 'UTF-8');