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>

client/src/pages/DashboardPage.tsx

@@ -1,15 +1,18 @@
+import React from "react";
 import { useAuth } from "../context/AuthContext";
 import { PageHeader } from "../components/PageHeader";
 
-const CARDS = [
-  { label: "Catalog", desc: "Products, categories, pricing", to: "/catalog" },
-  { label: "Users", desc: "Manage roles and access", to: "/users" },
-  { label: "Vendor", desc: "Business details and tax settings", to: "/vendor" },
-  { label: "Reports", desc: "Sales and tax summaries", to: "/reports" },
+const ALL_CARDS = [
+  { label: "Catalog", desc: "Products, categories, pricing",  to: "/catalog", roles: ["admin", "vendor", "user"] },
+  { label: "Events",  desc: "Events, tax overrides, reports", to: "/events",  roles: ["admin", "vendor"] },
+  { label: "Users",   desc: "Manage roles and access",        to: "/users",   roles: ["admin", "vendor"] },
+  { label: "Vendor",  desc: "Business details and tax settings", to: "/vendor", roles: ["admin", "vendor"] },
+  { label: "Reports", desc: "Sales and tax summaries",        to: "/reports", roles: ["admin", "vendor"] },
 ];
 
 export default function DashboardPage() {
   const { user } = useAuth();
+  const cards = ALL_CARDS.filter((c) => c.roles.includes(user?.role ?? ""));
 
   return (
     <div style={{ padding: "32px 28px", maxWidth: 900 }}>
@@ -18,7 +21,7 @@ export default function DashboardPage() {
         subtitle={`Welcome back, ${user?.name} · ${user?.vendorName}`}
       />
       <div style={grid}>
-        {CARDS.map((card) => (
+        {cards.map((card) => (
           <a key={card.label} href={card.to} style={cardStyle}>
             <div style={{ fontWeight: 600, marginBottom: 4 }}>{card.label}</div>
             <div style={{ color: "var(--color-text-muted)", fontSize: 13 }}>{card.desc}</div>