feat: add verify and docs to optimize AI coding

[tyler-dane]

Note

Low Risk
Low risk: primarily adds documentation and a new bun run verify helper script; runtime code changes are limited to comments and build/test tooling.

Overview
Adds a bun run verify command (packages/scripts/src/testing/verify.ts) that detects which workspace packages changed via git diff and runs only the relevant test:<pkg> suites followed by type-check.

Introduces AI/agent-focused documentation (CLAUDE.md, new docs/development/web-state-guide.md, and updates to docs/README.md and common-change-recipes.md) and adds clarifying header comments to key web state entry points (event.sagas.ts, store/events.ts, event.repository.util.ts).

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