docs(site): keep llms.txt synchronized with live benchmark data

[ramanbansal1]

What does this PR do?

Refactors llms.txt generation in src/clawbench/utils/update_llms.py to dynamically fetch live metadata, leaderboard data, canonical sitemap links, and CITATION.cff records. Adds unit and regression tests in tests/test_update_llms.py to ensure llms.txt stays strictly synchronized with live site data.

Resolves issues identified in #264:

• Corpus & Platform Metadata: Updated quick facts to reflect maintained V1 (153 tasks / 144 live websites) and V2 (130 tasks) counts.
• Dynamic Leaderboard Data: get_leaderboard_section() fetches live leaderboard data from https://claw-bench.com/api/leaderboard.json, generating V1 Hermes and V2 Hermes top 5 tables with pass rate, interception rate, and pass/total metrics.
• Canonical Routes from Sitemap: fetch_sitemap_urls() parses https://claw-bench.com/sitemap.xml to replace old hash routes with canonical URLs (/leaderboard, /tasks, /traces, /difficulty, etc.).
• Dataset Links: Added explicit canonical resource links for main task dataset (NAIL-Group/ClawBench), V1 execution traces (NAIL-Group/ClawBenchV1Trace), and V2 execution traces (TIGER-Lab/ClawBenchV2Trace).
• Citation Metadata: parse_citation_bibtex() parses CITATION.cff to automatically format BibTeX citations without manual drift.
• Regression Test: Added test_llms_txt_regression_check in tests/test_update_llms.py that fails if llms.txt diverges from live data/metadata generators.

Corpus

• v2
• v1
• both
• not applicable

Test plan

• Executed uv run python -m clawbench.utils.update_llms to update llms.txt from live sources and verified generated markdown output.
• Executed uv run pytest tests/test_update_llms.py (13 unit and regression test cases covering BibTeX parser, sitemap fetcher/fallback, leaderboard fetcher/fallback, quick facts, canonical resources, CLI dry-run, and workspace llms.txt regression check). All 13 tests passed.
• Executed full entrypoint test suite uv run pytest tests/test_cli_entrypoints.py tests/test_update_llms.py (18 tests passed).

Related issues

Fixes #264