fix(build): build @loopover/contract in ui:build, unbreaking the Cloudflare Workers build

The Workers build for loopover-ui has been failing on every PR since #9521
(merged as #9590) made src/openapi/schemas.ts import
@loopover/contract/public-api:

  Cannot find module '.../node_modules/@loopover/contract/dist/public-api.js'
    imported from /opt/buildhome/repo/src/openapi/schemas.ts

ui:build builds ui-kit and engine, then runs ui:openapi -- but never builds
the contract package, so the import resolves to a dist/ that does not
exist. CI did not catch it because the GitHub workflow has its own
separate "Build contract package" step (ci.yml:361) before the drift
checks; the Cloudflare build runs npm run build:cloudflare -> ui:build
directly and gets no such step. The two paths had silently diverged.

Add @loopover/contract to the same turbo invocation that already builds
the engine, so the one script both paths share produces everything
ui:openapi imports.

Reproduced locally by deleting packages/loopover-contract/dist and running
ui:openapi (identical ERR_MODULE_NOT_FOUND), then confirmed the fixed
chain builds the package and writes the spec with no drift.

Author: JSONbored

package.json

@@ -59,7 +59,7 @@
     "lint:composite-actions": "node --experimental-strip-types scripts/lint-composite-actions.ts",
     "ui:dev": "npm run ui:preview",
     "ui:kit:build": "npm run build --workspace @loopover/ui-kit",
-    "ui:build": "npm run ui:kit:build && turbo run build --filter=@loopover/engine && npm run ui:openapi && npm --workspace @loopover/ui run build && npm --workspace @loopover/ui-miner run build",
+    "ui:build": "npm run ui:kit:build && turbo run build --filter=@loopover/engine --filter=@loopover/contract && npm run ui:openapi && npm --workspace @loopover/ui run build && npm --workspace @loopover/ui-miner run build",
     "ui:preview": "npm run ui:build && wrangler dev --config apps/loopover-ui/dist/server/wrangler.json --ip 127.0.0.1 --port 4173 --local",
     "ui:lint": "npm run ui:kit:build && npm --workspace @loopover/ui-kit run format:check && npm --workspace @loopover/ui run format:check && npm --workspace @loopover/ui run lint && npm --workspace @loopover/ui-miner run format:check && npm --workspace @loopover/ui-miner run lint",
     "ui:typecheck": "npm run ui:kit:build && npm --workspace @loopover/ui run typecheck && npm --workspace @loopover/ui-miner run typecheck",