fix: audit findings — edge cases in paginate, output, run

- paginate.py: max(nums) on empty set → guard
- paginate.py: HEAD fallback to GET if server doesn't support HEAD
- output.py: disk health check every 500 topics
- run.py: avoid page-1 extra redirect
- __main__.py: URL validation (must contain vwts.ru)

vwts_scraper/paginate.py

@@ -44,7 +44,20 @@ def count(soup: BeautifulSoup) -> int:
         except ValueError:
             pass               # "…", "Назад", "Вперёд"
 
-    return max(nums) if nums else 1
+    return max(nums) if nums else 1     # защита от пустого pageNav
+
+
+def _head_or_get(session, url: str, timeout=(10, 30)) -> int:
+    """HEAD-запрос с fallback на GET (не все серверы поддерживают HEAD)."""
+    try:
+        r = session.head(url, timeout=timeout, allow_redirects=True)
+        if r.status_code in (405, 501):       # HEAD не поддерживается
+            r = session.get(url, timeout=timeout,
+                            allow_redirects=True, stream=True)
+            r.close()
+        return r.status_code
+    except Exception:
+        return 500
 
 
 def verify_last(section_url: str, claimed: int, session) -> int:
@@ -57,19 +70,16 @@ def verify_last(section_url: str, claimed: int, session) -> int:
         return claimed
 
     try:
-        import requests
-        r = session.head(f"{section_url}page-{claimed}",
-                         timeout=(10, 30), allow_redirects=True)
-        if r.status_code < 400:
+        status = _head_or_get(session, f"{section_url}page-{claimed}")
+        if status < 400:
             return claimed
 
-        # Бинарный поиск
+        # Бинарный поиск последней существующей страницы
         lo, hi = 1, claimed
         while lo < hi:
             mid = (lo + hi + 1) // 2
-            hr = session.head(f"{section_url}page-{mid}",
-                              timeout=(10, 30), allow_redirects=True)
-            if hr.status_code >= 400:
+            hr = _head_or_get(session, f"{section_url}page-{mid}")
+            if hr >= 400:
                 hi = mid - 1
             else:
                 lo = mid
@@ -78,4 +88,4 @@ def verify_last(section_url: str, claimed: int, session) -> int:
         return lo
 
     except Exception:
-        return claimed            # не смогли — верим сайту
+        return claimed