feat: add user role types and auth middleware

- lib/auth/roles.ts: UserRole union, ALL_ROLES, ROLE_HOME, getRoleHome, isValidRole (pure, no Supabase imports)
- __tests__/lib/auth/roles.test.ts: 8 TDD tests (written before implementation)
- middleware.ts: createServerClient with request.cookies pattern, unauthenticated redirect to /login, role-based redirect on / and /login

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AWxyMibCuGGtSQSqfajDQ7

lib/auth/roles.ts

@@ -0,0 +1,34 @@
+// lib/auth/roles.ts
+export type UserRole =
+  | 'reporter'
+  | 'supervisor'
+  | 'hse'
+  | 'capa_owner'
+  | 'management'
+  | 'admin'
+
+export const ALL_ROLES: UserRole[] = [
+  'reporter',
+  'supervisor',
+  'hse',
+  'capa_owner',
+  'management',
+  'admin',
+]
+
+export const ROLE_HOME: Record<UserRole, string> = {
+  reporter: '/reporter',
+  supervisor: '/supervisor',
+  hse: '/hse',
+  capa_owner: '/capa-owner',
+  management: '/management',
+  admin: '/admin',
+}
+
+export function getRoleHome(role: UserRole): string {
+  return ROLE_HOME[role]
+}
+
+export function isValidRole(value: unknown): value is UserRole {
+  return ALL_ROLES.includes(value as UserRole)
+}