Add anonymous public data spider

[xluos]

Summary

• Add public_spider.py as a CLI entrypoint for anonymous-cookie public data collection.
• Collect public user profile data, user videos, comments, and comment image URLs into JSON/JSONL outputs.
• Extend cookie generation so callers can pass a target URL, headless mode, timeout, and receive a reusable cookie string.
• Document the new anonymous public spider workflow and ignore generated outputs/ data.

Validation

• git diff --check origin/master..HEAD
• .venv/bin/python -m compileall public_spider.py utils/cookie_util.py
• .venv/bin/python public_spider.py --help