Add Smithers Fable Advisor workflow

[emo-eth]

Summary

• add a minimal .smithers workflow pack for the Fable Advisor orchestration pattern
• add a durable fable-advisor workflow that turns a work request into intake, CLI preflight, lane routing, a five-part implementer spec, advisor prompt, and verification contract
• document how to run the workflow from the README

Validation

• bunx smithers-orchestrator workflow list (discovers fable-advisor)
• cd .smithers && bun run typecheck
• bunx smithers-orchestrator graph .smithers/workflows/fable-advisor.tsx --compact --input '{"prompt":"Add rate limiting to the public API","risk":"correctness-critical","files":["src/api/**"],"interfaces":"Keep response bodies stable","verification":"npm test"}'
• SMITHERS_NO_REPORT=1 bunx smithers-orchestrator workflow run fable-advisor --input '{"prompt":"Add rate limiting to the public API","risk":"correctness-critical","files":["src/api/**"],"interfaces":"Keep response bodies stable","verification":"npm test"}' --format json --full-output

Smoke run completed as run ID 29f6221c-5d9a-47d1-a87b-1bf8495581e4 and returned status=ready, selectedLane=codex-implementer with explicit Grok-unavailable downgrade warning in this environment.