fix(ingest): raise ref cap to 50 and clarify invalid bvid error

tests/test_video_ref.py

@@ -63,6 +63,17 @@ def test_limit():
     assert len(extract_video_refs(text, limit=None)) == 3
 
 
+def test_default_cap_allows_bulk_paste():
+    from reaction_board.video_ref import DEFAULT_MAX_REFS
+
+    assert DEFAULT_MAX_REFS >= 15
+    text = " ".join(f"BV1x8x166E{i:02d}" for i in range(15))
+    assert len(extract_video_refs(text)) == 15
+    assert len(extract_video_refs(" ".join(
+        f"BV1x8x166E{i:02d}" for i in range(DEFAULT_MAX_REFS + 5)
+    ))) == DEFAULT_MAX_REFS
+
+
 def test_invalid_and_boundaries():
     assert extract_video_refs("") == []
     assert extract_video_refs(None) == []
@@ -85,6 +96,7 @@ def main():
     test_short_link()
     test_multiple_and_order_and_dedup()
     test_limit()
+    test_default_cap_allows_bulk_paste()
     test_invalid_and_boundaries()
     print("OK: 视频引用（BV/av/URL/短链）解析测试全部通过")