Expand template playbook

[Boyeep]

Summary

• expand template-playbook.md with a few generic starter-template patterns learned from the Go monorepo kit
• add public-template guidance for CODE_OF_CONDUCT.md and LICENSE
• add e2e and browser smoke coverage as first-class template-grade workflow patterns
• clarify that release automation can be built around either release-drafter or release-please
• extend the recommended file set, blueprint, and generic reuse rules to cover those cases

Why It Changed

• the playbook was already strong, but the Go template surfaced a few reusable infrastructure patterns worth keeping in the canonical guide
• these additions are generic starter-template concerns, not Go-specific or CV-specific behavior
• the goal is to make template-playbook.md a more complete one-stop reference for future templates

Verification

• npm run check:contract
• npm run check
• npm run check:images if Docker was available

Contract Impact

• no API contract changes
• updated docs/openapi.yaml
• ran npm run api:types
• updated frontend usage of generated types

Screenshots or Notes

• docs-only change
• no UI, backend, or workflow behavior changed in this PR