#5979: docs(anthropic): add ToS warning for setup-token usage

Anthropic's Consumer Terms of Service (Section 3) restricts automated access except via API Key. This adds a warning to help users understand the risks of using setup-tokens with third-party tools. Refs: - https://www.anthropic.com/legal/consumer-terms - Recent enforcement reports: https://www.reddit.com/r/ClaudeAI/comments/1qrgiuo/ <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates `docs/providers/anthropic.md` by adding a prominent “Terms of Service Notice” block under **Option B: Claude setup-token**, explaining that Anthropic’s Consumer ToS may restrict automated/non-human access except via an API key, and recommending **Option A (API Key)** for production/risk-averse usage. This fits the docs’ existing structure by clarifying the trade-offs between the two authentication options without changing any product behavior; it adds user-facing guidance where setup-token onboarding is documented. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - Documentation-only change that adds a warning block and does not affect runtime behavior; wording appears consistent with surrounding docs and introduces no build/test impact. - No files require special attention <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->