qol-sweep: OSS-readiness pass

[intel352]

Follow-up to the 2026-05-19 workflow QoL sweep, which left the visual-editor surface for a separate pass.

Checklist

• README polish (badges + 60-sec quickstart)
• CHANGELOG (Keep-a-Changelog) backfilled to latest tag
• CONTRIBUTING with local-dev quickstart (GOWORK=off where Go is involved)
• examples/ if applicable
• .github/ templates (issue + PR)

Refs

• Umbrella: docs: workflow main README polish + examples index + plugin templates workflow#714
• Sweep memory: project_qol_sweep_2026_05_19_shipped.md