Add per-check timeouts; increase Cloud Run timeout to 3600s

- run_check() wraps each check in a ThreadPoolExecutor future with a timeout
- Heavy checks: Image 180s, OCR 180s, Color Contrast 120s, veraPDF 120s
- Default per-check timeout: 90s
- Timed-out checks emit WARNING instead of hanging the whole request
- Cloud Run service timeout raised to 3600s (gcloud run services update)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

enterprise_pdf_checker.py

@@ -394,19 +394,43 @@ class EnterprisePDFChecker:
         )
         self.issues.append(issue)
     
+    # Per-check wall-clock timeouts (seconds). Heavy checks get more time.
+    _CHECK_TIMEOUTS = {
+        "Image Accessibility":       180,
+        "OCR Quality":               180,
+        "Color Contrast":            120,
+        "PDF/UA Structure (veraPDF)": 120,
+        "Content Readability":        60,
+    }
+    _DEFAULT_CHECK_TIMEOUT = 90
+
     def run_check(self, check_func, check_name: str) -> CheckResult:
-        """Run a check and record results"""
+        """Run a check with a per-check timeout and record results."""
+        from concurrent.futures import ThreadPoolExecutor, TimeoutError as FuturesTimeout
         start_time = time.time()
         result = CheckResult(check_name=check_name, passed=True)
         issues_before = len(self.issues)
+        timeout = self._CHECK_TIMEOUTS.get(check_name, self._DEFAULT_CHECK_TIMEOUT)
 
         try:
-            check_func()
+            with ThreadPoolExecutor(max_workers=1) as ex:
+                future = ex.submit(check_func)
+                future.result(timeout=timeout)
+
             # Check passed if no critical/error issues added by THIS check
             new_issues = self.issues[issues_before:]
             critical_errors = [i for i in new_issues
                              if i.severity in [Severity.CRITICAL, Severity.ERROR]]
             result.passed = len(critical_errors) == 0
+        except FuturesTimeout:
+            logger.warning(f"{check_name} timed out after {timeout}s — skipping")
+            self.add_issue(
+                Severity.WARNING,
+                check_name,
+                f"Check timed out after {timeout}s and was skipped",
+                details={'timeout': timeout}
+            )
+            result.passed = False
         except Exception as e:
             self.add_issue(
                 Severity.CRITICAL,
@@ -415,11 +439,11 @@ class EnterprisePDFChecker:
                 details={'error': str(e), 'traceback': traceback.format_exc()}
             )
             result.passed = False
-        
+
         result.duration = time.time() - start_time
         self.check_results.append(result)
         self.stats['total_checks'] += 1
-        
+
         return result
     
     def check_all(self) -> Dict[str, Any]: