Fix extract_visible_text to use proper byte position tracking (pos += char_len)
instead of iterating chars without position context, which caused script/style
tag detection to fail on multi-byte content. Also adds script/style stripping
logic and raises truncation limit to 10000 chars.
Adds 9 unit tests covering:
- Config identity verification
- OutputFormat serialization round-trip
- HTML text extraction (basic, script stripping, style stripping, empty input)
- Aggregate action with empty URLs
- CollectorAction deserialization (Collect/Aggregate/Extract)
- CollectionTarget deserialization
cc7ee3189d