feat: auth-aware UI and role-based access control (#67)

## Summary

- Add `is_admin` column to users table with Alembic migration and a `require_admin` FastAPI dependency that protects all admin-facing write endpoints (games, pokemon, evolutions, bosses, routes CRUD)
- Expose admin status to frontend via user API and update AuthContext to fetch/store `isAdmin` after login
- Make navigation menu auth-aware (different links for logged-out, logged-in, and admin users) and protect frontend routes with `ProtectedRoute` and `AdminRoute` components, preserving deep-linking through redirects
- Fix test reliability: `drop_all` before `create_all` to clear stale PostgreSQL enums from interrupted test runs
- Fix test auth: add `admin_client` fixture and use valid UUID for mock user so tests pass with new admin-protected endpoints

## Test plan

- [x] All 252 backend tests pass
- [ ] Verify non-admin users cannot access admin write endpoints (games, pokemon, evolutions, bosses CRUD)
- [ ] Verify admin users can access admin endpoints normally
- [ ] Verify navigation shows correct links for logged-out, logged-in, and admin states
- [ ] Verify `/admin/*` routes redirect non-admin users with a toast
- [ ] Verify `/runs/new` and `/genlockes/new` redirect unauthenticated users to login, then back after auth

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #67
Co-authored-by: Julian Tabel <juliantabel.jt@gmail.com>
Co-committed-by: Julian Tabel <juliantabel.jt@gmail.com>

backend/src/app/api/evolutions.py

@@ -3,6 +3,7 @@ from sqlalchemy import func, or_, select
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import joinedload
 
+from app.core.auth import AuthUser, require_admin
 from app.core.database import get_session
 from app.models.evolution import Evolution
 from app.models.pokemon import Pokemon
@@ -89,7 +90,9 @@ async def list_evolutions(
 
 @router.post("/evolutions", response_model=EvolutionAdminResponse, status_code=201)
 async def create_evolution(
-    data: EvolutionCreate, session: AsyncSession = Depends(get_session)
+    data: EvolutionCreate,
+    session: AsyncSession = Depends(get_session),
+    _user: AuthUser = Depends(require_admin),
 ):
     from_pokemon = await session.get(Pokemon, data.from_pokemon_id)
     if from_pokemon is None:
@@ -117,6 +120,7 @@ async def update_evolution(
     evolution_id: int,
     data: EvolutionUpdate,
     session: AsyncSession = Depends(get_session),
+    _user: AuthUser = Depends(require_admin),
 ):
     evolution = await session.get(Evolution, evolution_id)
     if evolution is None:
@@ -150,7 +154,9 @@ async def update_evolution(
 
 @router.delete("/evolutions/{evolution_id}", status_code=204)
 async def delete_evolution(
-    evolution_id: int, session: AsyncSession = Depends(get_session)
+    evolution_id: int,
+    session: AsyncSession = Depends(get_session),
+    _user: AuthUser = Depends(require_admin),
 ):
     evolution = await session.get(Evolution, evolution_id)
     if evolution is None:
@@ -164,6 +170,7 @@ async def delete_evolution(
 async def bulk_import_evolutions(
     items: list[BulkEvolutionItem],
     session: AsyncSession = Depends(get_session),
+    _user: AuthUser = Depends(require_admin),
 ):
     # Build pokeapi_id -> id mapping
     result = await session.execute(select(Pokemon.pokeapi_id, Pokemon.id))