feat: exclude_paths — skip dynamic areas (RSS feeds, news archives) from scan

Adds crawl.exclude_paths config option (list of URL path prefixes).
Matching URLs are excluded at two levels:
- Crawler: not fetched at all (saves HTTP requests)
- Differ: filtered from both baseline and current before comparison,
  so legacy baseline entries under excluded paths don't appear as
  "missing URLs" after the option is added retroactively

Example config:
  crawl:
    exclude_paths: ["/rss/", "/feed/", "/news/archiv/"]

8 new tests (176 total).

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

scanner/differ.py

@@ -12,6 +12,14 @@ from urllib.parse import urlparse
 # Normalisation
 # ---------------------------------------------------------------------------
 
+def _is_excluded(url: str, exclude_paths: list[str]) -> bool:
+    """Return True if the URL's path starts with any of the configured exclude prefixes."""
+    if not exclude_paths:
+        return False
+    path = urlparse(url).path
+    return any(path.startswith(ep) for ep in exclude_paths)
+
+
 def normalize_text(text: str, cfg: dict) -> str:
     """Apply noise-reduction before diffing."""
     norm_cfg = cfg.get("normalization", {})
@@ -103,6 +111,11 @@ def compare_snapshots(baseline_pages: dict, current_pages: dict, cfg: dict) -> d
       page_diffs (list of per-page change records),
       new_pages_analysis (freshly seen pages checked for immediate issues)
     """
+    excl = cfg.get("crawl", {}).get("exclude_paths", [])
+    if excl:
+        baseline_pages = {u: p for u, p in baseline_pages.items() if not _is_excluded(u, excl)}
+        current_pages  = {u: p for u, p in current_pages.items()  if not _is_excluded(u, excl)}
+
     b_urls = set(baseline_pages)
     c_urls = set(current_pages)