[Feature] Add pv stats - vault-wide analytics dashboard #1
Description
What to build:
- Total prompts, versions, evals run, avg overall score
- Top 3 highest scored prompts
- Most improved prompt (biggest score jump v1 → latest)
- Score distribution as ASCII bar chart
- All computed from existing SQLite data — no AI call needed
Files to touch: src/commands/ (new statsCmd.ts), src/db/queries.ts