[SCR-383] Auto-Mode (mode=auto) support

[kostas-jakeliunas-sb]

Merge order: part of the [SCR-383] Auto-Mode client rollout — merge once the server PR ScrapingBee/scrapingbee-API#1242 is merged + the flag is enabled.

tl;dr

Docs-only change so a LangChain agent can choose ScrapingBee Auto-Mode (mode=auto). The tools already spread arbitrary params into the request, so mode/max_cost work today — the LLM just won't select them until the tool docstring lists them. No request-code or architecture change; no validation added.

Summary

• langchain_scrapingbee/tools.py — added mode and max_cost to ScrapeUrlTool's LLM-facing docs so an agent will pick Auto-Mode:
  • new mode + max_cost entries in the SUPPORTED PARAMS list (the existing UNSUPPORTED PARAMS: anything not listed clause now permits them);
  • a short prose hint at the top of the tool description ("when unsure which config a site needs, prefer mode='auto'…");
  • a {"mode": "auto", "max_cost": 25} example in the ScrapeUrlInput.params field description.
  • Accurate contract documented: mode='auto' is GET-only, cheapest→expensive, charges only the winning config (0 on full failure), reports credits via the Spb-auto-cost response header, and must not be combined with render_js/premium_proxy/stealth_proxy/transparent_status_code; max_cost (int ≥ 1) caps spend and requires mode='auto'.
• README.md — added an Auto-Mode usage example (Test Case 1b) mirroring the existing examples, passing params={"mode":"auto","max_cost":25} to ScrapeUrlTool.
• pyproject.toml / release_notes.md — bumped 0.2.0 → 0.2.1 and added a changelog entry (matches the repo's version-field + release_notes.md convention; repo has no git tags).

Test plan

• pytest --disable-socket unit suite — 90 passed (no code path changed; docstrings/version only).
• python -c "ast.parse(...)" — tools.py compiles.
• ruff check — net +3 E501 (long-line) only, matching this file's prevailing one-line-per-param docstring style (177 pre-existing E501; repo lint baseline is already non-clean and ungated). No new rule classes introduced.
• Integration tests (make integration_tests) require a live SCRAPINGBEE_API_KEY and the server Auto-Mode flag enabled — run when the server feature ships (this is why the PR stays draft).
• Manual: agent picks mode='auto' for an unknown site and Spb-auto-cost reflects the winning tier.

🤖 Generated with Claude Code