feat(export): CSV export for bookings and customers

GET /v1/export/bookings.csv (optional from/to bounds) and
/v1/export/customers.csv — UTF-8 with BOM for Excel, labels resolved
at export time, buffered responses so auth failures stay JSON.
Export buttons on the bookings and customers pages.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/frontend/src/routes/dashboard/bookings-page.tsx

@@ -5,6 +5,7 @@ import { Textarea } from "../../components/ui/textarea";
 import { getInitials } from "../../components/dashboard/types";
 import { CalendarDaysIcon, PlusIcon, XIcon, EyeIcon } from "../../components/dashboard/icons";
 import { apiClient } from "../../lib/api-client";
+import { ExportCsvButton } from "../../components/dashboard/export-csv-button";
 import { DashboardLayout, useDashboardData } from "./layout";
 
 function BookingsPage() {
@@ -123,9 +124,12 @@ function BookingsPage() {
           <h1 class="text-2xl sm:text-3xl font-bold text-ink font-display">{data.i18n.t("dashboard.bookingManagement")}</h1>
           <p class="text-ink-muted mt-1">{bookingStats().total} {data.i18n.t("dashboard.totalBookings")}</p>
         </div>
-        <button onClick={() => setShowNewBooking(true)} class="btn-primary text-sm shrink-0">
-          <PlusIcon /> {data.i18n.t("dashboard.newBooking")}
-        </button>
+        <div class="flex items-center gap-2 shrink-0">
+          <ExportCsvButton path="/v1/export/bookings.csv" filename="bookra-bookings.csv" token={data.token} />
+          <button onClick={() => setShowNewBooking(true)} class="btn-primary text-sm">
+            <PlusIcon /> {data.i18n.t("dashboard.newBooking")}
+          </button>
+        </div>
       </div>
 
       {/* Stats */}

apps/frontend/src/routes/dashboard/customers-page.tsx

@@ -1,5 +1,6 @@
 import { Show, createSignal, createMemo, createResource } from "solid-js";
 import { apiClient } from "../../lib/api-client";
+import { ExportCsvButton } from "../../components/dashboard/export-csv-button";
 import { Input } from "../../components/ui/input";
 import { getInitials } from "../../components/dashboard/types";
 import { UsersIcon, XIcon } from "../../components/dashboard/icons";
@@ -73,6 +74,7 @@ function CustomersPage() {
           <h1 class="text-2xl sm:text-3xl font-bold text-ink font-display">{data.i18n.t("dashboard.customers")}</h1>
           <p class="text-ink-muted mt-1">{filteredCustomers().length} {data.i18n.locale() === "cs" ? "zákazníků" : "customers"}</p>
         </div>
+        <ExportCsvButton path="/v1/export/customers.csv" filename="bookra-customers.csv" token={data.token} />
       </div>
       <div class="surface-card p-4">
         <Input type="text" placeholder={data.i18n.t("dashboard.search.customers")} value={searchQuery()} onInput={(e) => setSearchQuery(e.currentTarget.value)} />