POL-124: Migrate frontend from React Native to Next.js web app

- Replace mobile/ (Expo) with web/ (Next.js 16 + Tailwind + shadcn/ui)
- Pages: login, register, pending, championships, championship detail, registrations, profile, admin
- Logic/view separated: hooks/ for data, components/ for UI, pages compose both
- Types in src/types/ (one interface per file)
- Auth: Zustand store + localStorage tokens + cookie presence flag for proxy
- API layer: axios client with JWT auto-refresh

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

CLAUDE.md

@@ -10,8 +10,8 @@ Current implementation is a simplified MVP working toward that goal.
 # Backend
 cd backend && .venv/Scripts/python -m uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload
 
-# Mobile (set BASE_URL in src/api/client.ts to LAN IP first)
-cd mobile && npx expo start --lan --clear
+# Web frontend
+cd web && npm run dev   # runs on http://localhost:3000
 
 # Seed test data
 cd backend && .venv/Scripts/python seed.py
@@ -20,7 +20,7 @@ cd backend && .venv/Scripts/python seed.py
 ## Current Architecture
 
 - **Backend**: FastAPI + SQLAlchemy 2 (async) + aiosqlite (SQLite dev) + Alembic + bcrypt
-- **Mobile**: Expo (blank-typescript) + React Navigation v6 + Zustand + Axios + Ionicons
+- **Web**: Next.js 15 (App Router) + Tailwind CSS + shadcn/ui + TanStack Query + Zustand
 - **Auth**: JWT access (15min) + refresh token rotation (7 days, SHA-256 hashed in DB)
 
 ## Project Layout
@@ -29,10 +29,11 @@ cd backend && .venv/Scripts/python seed.py
 backend/app/           FastAPI app (models, schemas, routers, crud, services)
 backend/alembic/       Async migrations
 backend/.venv/         Virtual env (use .venv/Scripts/python)
-mobile/src/api/        Axios client + API modules (auth, championships, users)
-mobile/src/store/      Zustand auth store
-mobile/src/screens/    auth/, championships/, admin/, profile/
-mobile/src/navigation/ RootNavigator -> AuthStack | AppStack (Tabs + Detail)
+web/src/app/           Next.js App Router pages
+web/src/lib/api/       Axios client + API modules (auth, championships, users)
+web/src/store/         Zustand auth store
+web/src/components/    Shared UI components
+web/src/middleware.ts  Route protection
 dancechamp-claude-code/ Target spec: SPEC.md, PLAN.md, DATABASE.md, DESIGN-SYSTEM.md, SCREENS.md
 ```
 
@@ -41,9 +42,8 @@ dancechamp-claude-code/ Target spec: SPEC.md, PLAN.md, DATABASE.md, DESIGN-SYSTE
 - **passlib + bcrypt 5.x incompatible** — use `bcrypt` directly (NOT passlib)
 - **Circular import**: auth_service.py must NOT import crud_user
 - **SQLAlchemy UUID**: Use `sqlalchemy.Uuid(as_uuid=True)` not `postgresql.UUID`
-- **Expo newArchEnabled: true** crashes Expo Go — keep `false` in app.json
 - **Stale uvicorn**: Kill with `powershell.exe -NoProfile -Command "Get-Process python | Stop-Process -Force"`
-- **BASE_URL**: mobile/src/api/client.ts must use LAN IP (not localhost) for physical devices
+- **Web API URL**: set `NEXT_PUBLIC_API_URL` in `web/.env.local` (default: http://localhost:8000/api/v1)
 
 ## Test Credentials (run seed.py)
 
@@ -64,12 +64,25 @@ member@pole.dev / Member1234     (member, approved)
 ## Code Conventions
 
 - Backend: Pydantic v2 schemas, async SQLAlchemy, `from_attributes = True`
-- Mobile: Functional components, Zustand stores, Ionicons for icons
+- Web: Functional components, TanStack Query for server state, Zustand for auth, shadcn/ui components
 - Registration: members auto-approved, organizers require admin approval
-- Tab navigator uses `headerShown: true` for safe area; no manual headings in tab screens
 
 ## Environment
 
 - Windows 10, Python 3.12, Node.js
 - Docker NOT installed, PostgreSQL NOT installed (use SQLite for dev)
 - venv always in backend/.venv
+
+## Linear Workflow (MANDATORY)
+
+**Every action** (coding, migrations, docs, planning, bug fixes) MUST have a Linear issue.
+
+Before starting ANY task:
+1. Check if a matching Linear issue exists in the "Pole dance app" workspace
+2. If not — create one (title, description, priority)
+3. Set status to **In Progress** before writing any code
+
+After completing:
+- Set status to **Done**
+- Make a git commit with message: `POL-N: <task title>`
+- Report the issue number to the user (e.g. "Done — POL-42")