Add roles and users admin UI with role management API

Backend:
- GET /v1/users (list company users)
- GET/POST/PATCH/DELETE /v1/roles (role CRUD with permissions)
- GET/POST/DELETE /v1/users/:userId/roles (role assignment)
- GET /v1/me/permissions (current user's effective permissions)

Frontend:
- Roles list page with kebab menu (edit permissions, delete custom)
- Role detail page with grouped permission checkboxes and inheritance note
- New role page with auto-generated slug
- Users list page showing assigned roles per user
- Manage Roles dialog for adding/removing roles per user
- Sidebar: Admin section with Users, Roles, Help links

packages/backend/src/main.ts

@@ -14,6 +14,7 @@ import { inventoryRoutes } from './routes/v1/inventory.js'
 import { productRoutes } from './routes/v1/products.js'
 import { lookupRoutes } from './routes/v1/lookups.js'
 import { fileRoutes } from './routes/v1/files.js'
+import { rbacRoutes } from './routes/v1/rbac.js'
 
 export async function buildApp() {
   const app = Fastify({
@@ -62,6 +63,7 @@ export async function buildApp() {
   await app.register(productRoutes, { prefix: '/v1' })
   await app.register(lookupRoutes, { prefix: '/v1' })
   await app.register(fileRoutes, { prefix: '/v1' })
+  await app.register(rbacRoutes, { prefix: '/v1' })
 
   return app
 }