Vendor-assign events and scope event catalog to vendor

- Add vendorWhereClause() helper: admin + ?vendorId= filters to that
  vendor; admin with no filter sees all; other roles locked to own
- Fix events GET / to use vendorWhereClause so vendor filter works
- EventFormModal: admin sees a Vendor picker when creating a new event,
  pre-populated from the active VendorFilter; POST includes ?vendorId=
- EventConfigPanel: scope /taxes and /products fetches to event.vendorId
  so only the event's vendor's catalog items are selectable

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

client/src/pages/EventsPage.tsx

@@ -5,7 +5,7 @@ import { PageHeader } from "../components/PageHeader";
 import { VendorFilter } from "../components/VendorFilter";
 import { Table } from "../components/Table";
 import { Modal } from "../components/Modal";
-import { FormField, Btn } from "../components/FormField";
+import { FormField, Btn, inputStyle } from "../components/FormField";
 
 // ─── Types ──────────────────────────────────────────────────────────────────
 
@@ -139,6 +139,7 @@ export default function EventsPage() {
       {showForm && (
         <EventFormModal
           event={editing}
+          defaultVendorId={vendorId}
           onClose={() => setShowForm(false)}
           onSaved={() => { setShowForm(false); load(); }}
         />
@@ -159,20 +160,39 @@ export default function EventsPage() {
 
 // ─── Event Form Modal ────────────────────────────────────────────────────────
 
-function EventFormModal({ event, onClose, onSaved }: {
+function EventFormModal({ event, defaultVendorId, onClose, onSaved }: {
   event: Event | null;
+  defaultVendorId?: string;
   onClose: () => void;
   onSaved: () => void;
 }) {
+  const { user } = useAuth();
+  const isAdmin = user?.role === "admin";
   const [name, setName] = useState(event?.name ?? "");
   const [description, setDescription] = useState(event?.description ?? "");
   const [startsAt, setStartsAt] = useState(event ? toDatetimeLocal(event.startsAt) : "");
   const [endsAt, setEndsAt] = useState(event ? toDatetimeLocal(event.endsAt) : "");
   const [isActive, setIsActive] = useState(event?.isActive ?? true);
+  const [selectedVendorId, setSelectedVendorId] = useState(
+    event?.vendorId ?? defaultVendorId ?? ""
+  );
+  const [vendors, setVendors] = useState<Vendor[]>([]);
   const [error, setError] = useState("");
   const [saving, setSaving] = useState(false);
 
+  useEffect(() => {
+    if (isAdmin && !event) {
+      api.get<{ data: Vendor[] }>("/vendors?limit=200")
+        .then((r) => setVendors(r.data))
+        .catch(console.error);
+    }
+  }, [isAdmin, event]);
+
   const save = async () => {
+    if (isAdmin && !event && !selectedVendorId) {
+      setError("Please select a vendor for this event.");
+      return;
+    }
     setSaving(true);
     setError("");
     try {
@@ -185,7 +205,8 @@ function EventFormModal({ event, onClose, onSaved }: {
       if (event) {
         await api.put(`/events/${event.id}`, body);
       } else {
-        await api.post("/events", body);
+        const q = isAdmin && selectedVendorId ? `?vendorId=${encodeURIComponent(selectedVendorId)}` : "";
+        await api.post(`/events${q}`, body);
       }
       onSaved();
     } catch (err) {
@@ -197,6 +218,15 @@ function EventFormModal({ event, onClose, onSaved }: {
 
   return (
     <Modal title={event ? "Edit Event" : "New Event"} onClose={onClose}>
+      {isAdmin && !event && (
+        <FormField label="Vendor" required>
+          <select style={inputStyle} value={selectedVendorId}
+            onChange={(e) => setSelectedVendorId(e.target.value)} required>
+            <option value="">Select vendor…</option>
+            {vendors.map((v) => <option key={v.id} value={v.id}>{v.name}</option>)}
+          </select>
+        </FormField>
+      )}
       <FormField label="Name">
         <input style={input} value={name} onChange={(e) => setName(e.target.value)} />
       </FormField>
@@ -276,11 +306,12 @@ function EventConfigPanel({ event, onRefresh }: { event: Event; onRefresh: () =>
   const [err, setErr] = useState("");
 
   useEffect(() => {
+    const q = `?vendorId=${encodeURIComponent(event.vendorId)}&limit=200`;
     Promise.all([
-      api.get<ApiList<Tax>>("/taxes?limit=100").then((r) => setTaxes(r.data)),
-      api.get<ApiList<Product>>("/products?limit=200").then((r) => setProducts(r.data)),
+      api.get<ApiList<Tax>>(`/taxes${q}`).then((r) => setTaxes(r.data)),
+      api.get<ApiList<Product>>(`/products${q}`).then((r) => setProducts(r.data)),
     ]).catch(console.error);
-  }, []);
+  }, [event.vendorId]);
 
   const addTax = async () => {
     setErr("");