MVP: Stabilize install, type-check, and common build

[kuyacarlo]

Parent: #14

Bottom line

Unblock the tree: fix type-check failures (Jest globals in web tests), ensure @worksight/common builds and is consumable by web/api.

Done means

• pnpm --filter @worksight/common build green
• pnpm --filter @worksight/web type-check green
• pnpm --filter @worksight/api type-check green
• Documented install/dev commands in README

[kuyacarlo]

Handoff: https://github.com/4sightorg/worksight/blob/docs/mvp-handoffs/docs/handoffs/2026-07-25-stabilize-typecheck.md

[kuyacarlo]

Started on feat/mvp-stabilize: excluded src/__tests__ from web tsconfig so type-check passes. common build + web/api type-check green locally.