feat(config): add per-model edit capability

[ncxton]

Summary

• add per-model models.<id>.edit config and config set support
• persist edit capability after interactive model selection/auth add
• require configured edit capability for potaco edit while keeping generation assumed available
• remove discovered capability labels from model listing/picker output and update docs/skills

Test Plan

• go test ./...
• go vet ./...
• gofmt -l .