feat(performance): per-job score cache to avoid re-scoring unchanged jobs

[bjridicodes]

If a job's (title, company, description) hash hasn't changed since last scoring, reuse cached score. Saves tokens on re-runs that find existing jobs.

[bjridicodes]

Relationships

Depends on:

• feat(resilience): LLM output schema validation with retry #30 — score cache requires Pydantic-validated outputs to be safe to cache; malformed outputs must not be persisted