[Feature] Include content URLs by default in URL API calls

[Feature] Include content URLs by default in URL API calls

- Add `include_content_urls` global option (default: true) to control
  whether URLs extracted from content (PDF, etc.) are included in API calls
- Update task:get_urls(), task:get_emails() to include content URLs by default
- Update lua_util.extract_specific_urls() to use config default when
  need_content is not explicitly specified
- Mark URLs extracted from computed/virtual parts (PDF text) with CONTENT
  flag instead of FROM_TEXT flag, since they may be clickable links
- Add commented documentation in conf/options.inc

Users who want the old behavior can set `include_content_urls = false`
in their options configuration.