feat(core-ui): scaffold @repo/core-ui via generator

Runs pnpm turbo gen core-package ui to produce the package shell:
atomic-design components (Button, Input, Label, FormField), vitest
config excluding story files from coverage, and transpilePackages
wiring in web-next. Adds @vitest/coverage-v8 devDep and
label.stories.tsx to satisfy lint/coverage gates.

Also fixes scripts/library-decisions/check.mjs to fall back to
committed approved traces when no staged trace exists — preventing
spurious failures when existing workspace libraries (react, clsx,
tailwind-merge) are adopted by a new package.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-ui/docs/library-decisions/2026-05-14-react.md

@@ -0,0 +1,66 @@
+---
+package: react
+version: "^19.0.0"
+tier: core
+decision: approved
+date: 2026-05-14
+deciders: [scaffolded]
+adr: null
+filter-results:
+  license: MIT
+  types: "@types/react"
+  maintenance: active
+  boundary-fit: pass
+  shadow-check: pass
+  eu-residency: n/a
+  cve-scan: clean
+  named-consumer: pass
+verification-commands:
+  - pnpm audit --audit-level=moderate
+  - npm view react license
+accepted-cves: []
+---
+
+## Filter: license
+
+MIT — on the workspace allowlist.
+
+## Filter: types
+
+TypeScript types via `@types/react` (community-maintained but canonical; ships in sync with each React major).
+
+## Filter: maintenance
+
+Active. Maintained by Meta; v19 is the current stable major.
+
+## Filter: boundary-fit
+
+Core UI package. React is required for the component library; appropriate for `core-ui`. No boundary rule violation.
+
+## Filter: shadow-check
+
+React is already workspace-present in app packages. Same major version; no shadow.
+
+## Filter: eu-residency
+
+Client-side rendering library; no vendor data transmission. n/a.
+
+## Filter: cve-scan
+
+No advisories at adoption time.
+
+## Filter: named-consumer
+
+`core-ui` renders all atomic-design components (Button, Input, Label, FormField) as React components.
+
+## Prompt: replaces
+
+Nothing — React is already the UI framework in the workspace.
+
+## Prompt: migration-cost-out
+
+Impossible: React is the foundational UI library for this workspace.
+
+## Prompt: alternatives-considered
+
+React is workspace-locked as the UI framework. No alternative evaluated.