fix: allow dots in repo names for checkout validation

GitHub repos like interserver/webhooks.interserver.net contain dots
but the checkoutBranch regex only allowed alphanumerics, underscores
and hyphens. Update regex to also allow dots and forward slashes
in owner/repo components.

Author: detain

scripts/github-code-review.php

@@ -1049,7 +1049,7 @@ function checkoutBranch(string $repo, string $branch, string $checkoutPath): str
     verbose_log("checkoutBranch: repo={$repo} branch={$branch} path={$checkoutPath}", 3);
 
     // Validate repo format to prevent path traversal
-    if (!preg_match('/^[a-zA-Z0-9_-]+\/[a-zA-Z0-9_-]+$/', $repo)) {
+    if (!preg_match('/^[a-zA-Z0-9_.\/-]+\/[a-zA-Z0-9_.\/-]+$/', $repo)) {
         verbose_log("checkoutBranch: invalid repo format: {$repo}", 1);
         return 'invalid repo format';
     }

tests/phpunit/unit/Cli/Renderer/TableRendererTest.php

@@ -226,8 +226,8 @@ public function testSeverityIcons(): void
         $this->renderer->renderStatusItem($output, $status);
 
         $content = $output->fetch();
-        // Error severity should show red circle emoji
-        $this->assertStringContainsString("\xE2\x9D\x94", $content);
+        // Error severity should show red circle emoji (U+1F534)
+        $this->assertStringContainsString("\xF0\x9F\x94\xB4", $content);
     }
 
     public function testStatusIcons(): void