Clarify scope in README title and description

[davidahmann]

Updated README to specify 'Production AI Agent Tool Calls'.

Summary

Testing

• make fmt
• make lint
• make test

Hardening Review

• Failure classification impact reviewed (error_category, error_code, retryability)
• Exit code contract impact reviewed (no accidental contract break)
• Deterministic output impact reviewed (--json, artifacts, golden fixtures)
• Security/privacy impact reviewed (secrets redaction, key handling, fail-closed behavior)

Operational Notes

• User-facing docs updated where behavior changed (README.md, docs/hardening/*, runbooks)
• Docs sync checked across onboarding surfaces (README.md, docs/README.md, docs-site/public/llm/*, docs-site/public/llms.txt)
• New docs pages added to discoverability surfaces (docs-site/src/lib/navigation.ts, docs-site/src/app/docs/page.tsx, docs-site/public/sitemap.xml)
• Terminology changes reconciled in canonical definition pages (tool boundary + capability taxonomy)
• If agent behavior touched production-like paths, attached runpack evidence (If your agent touched prod, attach the runpack.)
• Included ticket footer evidence line (gait run receipt --from <run_id|path>)
• For new/expanded official integration lane proposals, attached gait-out/integration_lane_scorecard.json evidence and decision outcome