Create agentic workflow for extracting prompt improvement suggestions based on merged PRs

`update-instructions-from-pr-reviews` SKILL

- Can be run locally or used in an agentic workflow
- Mines merged PRs from the upstream repo (if on a fork) for a custom time range. Check cache to avoid re-processing
- outputs a JSON of findings. JSON will be aggregable into a SQL database for metric extraction
- Rely on agent to leverage skill and orchestrate deterministic TS scripts

desired DB schema

JSON schema

## open question

- specific agentic workflow per-repo? or a common one synced from tools?