Rename roles, add multi-vendor support, and Events system

Roles: owner→admin, manager→vendor, cashier→user across all routes,
seed, and client UI. Role badge colours updated in UsersPage.

Multi-vendor:
- GET /vendors and GET /users now return all records for admin role;
  vendor/user roles remain scoped to their vendorId
- POST /users: admin can specify vendorId to assign user to any vendor
- vendors/users now include vendor name in responses for admin context

Events (new):
- Prisma schema: Event, EventTax, EventProduct models; Transaction.eventId
- POST/GET/PUT/DELETE /api/v1/events — full CRUD, vendor-scoped
- PUT /events/:id/taxes + DELETE — upsert/remove per-event tax rate overrides
- POST/GET/DELETE /events/:id/products — product allowlist (empty=all)
- GET /events/:id/transactions — paginated list scoped to event
- GET /events/:id/reports/summary — revenue, avg tx, top products for event
- Transactions: eventId accepted in both single POST and batch POST
- Catalog sync: active/upcoming events included in /catalog/sync response

Client:
- Layout nav filtered by role (user role sees Catalog only)
- Dashboard cards filtered by role
- Events page: list, create/edit modal, detail modal with Configuration
  (tax overrides + product allowlist) and Reports tabs

DB: DATABASE_URL updated to file:./prisma/dev.db in .env.example

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

server/prisma/seed.ts

@@ -5,20 +5,20 @@ const prisma = new PrismaClient();
 
 async function main() {
   // Seed roles
-  const ownerRole = await prisma.role.upsert({
-    where: { name: "owner" },
+  const adminRole = await prisma.role.upsert({
+    where: { name: "admin" },
     update: {},
-    create: { name: "owner" },
+    create: { name: "admin" },
   });
   await prisma.role.upsert({
-    where: { name: "manager" },
+    where: { name: "vendor" },
     update: {},
-    create: { name: "manager" },
+    create: { name: "vendor" },
   });
   await prisma.role.upsert({
-    where: { name: "cashier" },
+    where: { name: "user" },
     update: {},
-    create: { name: "cashier" },
+    create: { name: "user" },
   });
 
   // Seed demo vendor
@@ -32,7 +32,7 @@ async function main() {
     },
   });
 
-  // Seed demo owner user
+  // Seed demo admin user
   await prisma.user.upsert({
     where: { email: "admin@demo.com" },
     update: {},
@@ -41,7 +41,7 @@ async function main() {
       passwordHash: await bcrypt.hash("password123", 10),
       name: "Demo Admin",
       vendorId: vendor.id,
-      roleId: ownerRole.id,
+      roleId: adminRole.id,
     },
   });