docs: refresh engineering runbooks

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Summary

• Correct setup guidance for explicit Prisma client generation and npm run dev/nodemon usage.
• Refresh engineering notes for the current event-loader contracts and release workflow tag-existence gate.
• Expand the contributor test inventory for event-loader, cooldown, and rank-card regressions.

Codepaths Covered

• package.json scripts and absence of a postinstall hook
• src/handlers/events.js and src/utils/getAllFiles.js
• .github/workflows/release.yml
• tests/events-handler-shape.test.js, tests/interaction-cooldown.test.js, and tests/rank-card-presence-status.test.js

Key Knowledge Gaps Addressed

• Prisma client generation is manual after install/schema changes.
• npm run dev requires nodemon to be available.
• Release creation is gated by the missing v<package.version> tag, not by a package version-line diff.
• Guild event modules with { event, run } are valid and covered by regression tests.

Validation

• git diff --check HEAD~1..HEAD
• npm test (37 passed)