refactor: remove core-ui from main (scaffoldable via gen core-package ui)

Removal across all three consumers:
- apps/storybook: strips @repo/core-ui dep, clears stories glob (now []),
  removes globals.css import from preview.ts
- apps/web-next: strips @repo/core-ui dep + transpilePackages entry
- apps/web-tanstack: strips @repo/core-ui dep
- packages/core-ui: deleted entirely (28 files)

No app pages needed surgery — neither web-next nor web-tanstack source
files imported @repo/core-ui directly. The storybook app referenced it
only via the stories glob and the globals.css preview import.

Gates: 40/40 tasks successful, all 4 e2e byte-identical reconstructions
pass (realtime, events, trpc, ui).

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

packages/core-ui/AGENTS.md

@@ -1,67 +0,0 @@
-# AGENTS.md — core-ui
-
-Design-system primitives organized by Atomic Design. Only **generic components** (atoms, molecules, generic organisms) live here. Feature-specific components live in their respective feature packages.
-
-## Responsibilities
-
-- **Atoms** — Single HTML elements: Button, Input, Label, Card
-- **Molecules** — Combinations: FormField (Label + Input), Badge, Avatar
-- **Generic Organisms** — Reusable complex layouts: Modal, Tabs, NavigationMenu, CommandPalette
-- **Templates** — Page layouts: AuthLayout, DashboardLayout, LandingLayout
-- **Utilities** — `cn()` for className merging, design tokens, Tailwind config
-
-## Feature-specific boundary
-
-Feature-specific organisms (e.g., `ArticleCard`, `ArticleList`, `HeaderNavMenu`) live in their feature's `ui/` folder, NOT here. This boundary keeps `core-ui` framework-agnostic and reusable.
-
-## Must NOT import
-
-- Any feature package (`@repo/auth`, `@repo/blog`, etc.)
-- Any app package
-- `@repo/core-api`, `@repo/core-cms`, `@repo/core-trpc`
-
-> Note: `@repo/core-trpc` is an optional package scaffolded via `pnpm turbo gen core-package trpc`. If not present, this constraint still applies to any future installation.
-
-## Public exports
-
-From `package.json`:
-- `.` — all atoms, molecules, organisms, templates
-
-Example usage:
-```typescript
-import { Button, Input, Label } from "@repo/core-ui";
-import { FormField } from "@repo/core-ui";
-import { Modal, Tabs } from "@repo/core-ui";
-```
-
-## Test conventions
-
-- Tests colocated: `src/atoms/button/button.tsx` → `src/atoms/button/button.test.tsx`
-- Vitest environment: `jsdom` (React component testing)
-- Alias: `@/` resolves to `src/`
-- Run: `pnpm test --filter @repo/core-ui`
-- Storybook stories colocated: `src/atoms/button/button.stories.tsx`
-
-## Structure
-
-```
-src/
-  atoms/
-    {name}/
-      {name}.tsx             # Component
-      {name}.test.tsx        # Tests
-      {name}.stories.tsx     # Storybook story
-      index.ts               # Barrel export
-  molecules/
-    {name}/
-      ...
-  organisms/
-    {name}/
-      ...
-  templates/
-    {name}/
-      ...
-  lib/
-    utils.ts                 # cn() and helpers
-  index.ts                   # Re-exports everything
-```