add antibot guard and retry

iaai_scraper/core/exceptions.py

@@ -0,0 +1,10 @@
+class ScraperError(Exception):
+    """Base scraper exception."""
+
+
+class AntiBotDetectedError(ScraperError):
+    """Raised when the target website appears to block automation."""
+
+
+class SiteStructureChangedError(ScraperError):
+    """Raised when the page shape changed and required data is missing."""