feat: unify vitest config with projects pattern

[dmmulroy]

Problem

1. no unified test runner - each package runs tests independently, no single command
2. version drift - packages have different vitest versions, subtle incompatibilities
3. deprecated workspace config - using vitest.workspace (deprecated in 3.2)
4. no shared config - timeout/globals duplicated across packages
5. pool-workers version lock - @cloudflare/vitest-pool-workers only supports 2.0.x-3.2.x

Solution

root vitest.config.ts orchestrates all package tests via projects config. shared settings in vitest.shared.ts. syncpack keeps versions aligned. pinned to vitest 3.2.4 until pool-workers supports 4.x.

Changes

• add root vitest.config.ts with projects config
• add vitest.shared.ts for common test settings
• update packages/core and packages/storage to use shared
• exclude vitest configs and test dirs from packages/tsconfig.json (build was failing)
• downgrade vitest to 3.2.4 (pool-workers incompatible w/ 4.x)
• add syncpack for version sync

Verification

• pnpm test:run - 17 tests pass (core + storage)
• pnpm test:ui - UI launches at localhost:51204