Docs: fix stale agent metadata references

[nerdchanii]

Summary

• replace the deleted public agent guide reference in llms.txt
• repoint docs/agents/agent-context.json to the remaining agent examples reference
• update the provider example anchor to the renamed public examples heading

Context

• follow-up to post-merge Codex review comments on Docs: remove agent and internal content from public docs #121 and Docs: rewrite the examples page around user scenarios #123

Verification

• node -e "JSON.parse(require('fs').readFileSync('docs/agents/agent-context.json', 'utf8'))"
• npm run docs:build
• npm run lint

[nerdchanii]

@codex review

Context:

• Follow-up to missed post-merge review comments from Docs: remove agent and internal content from public docs #121 and Docs: rewrite the examples page around user scenarios #123
• Scope: only stale agent metadata references and the renamed examples anchor

[chatgpt-codex-connector]

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