feat(invoices): full invoice + line items module

The most complex module. Two-table model: invoices (header) +
invoice_items (lines). Auto-numbering via tenant_settings.invoiceCounter,
auto-totals on item changes.

Schema/validation:
- lib/validation/invoices.ts: invoiceSchema (header) + invoiceItemSchema
  (line). Both coerce comma decimals.
- lib/appwrite/invoice-actions.ts:
  * createInvoiceAction — fetches tenant_settings, increments
    invoiceCounter, formats number as '{prefix}-{year}-{0000}',
    persists totals as 0/0/0 (recomputed when items added).
  * updateInvoiceAction / deleteInvoiceAction — header CRUD; delete
    cascades to remove all items first then header.
  * addInvoiceItemAction / updateInvoiceItemAction /
    deleteInvoiceItemAction — line CRUD. Each computes lineTotal
    (qty*unit + vat) and triggers recomputeTotals(invoiceId) which
    re-sums all items and updates the header subtotal/vatTotal/total.
  All audit-logged.

Queries:
- listInvoices, getInvoice (with tenant cross-check), listInvoiceItems.

UI:
- /invoices index: 4 stat cards (Toplam / Tahsil edildi / Bekleyen /
  Gecikmiş), table with overdue-aware due date coloring, status badges,
  number is a Link to detail.
- InvoiceFormSheet: customer + dates (default issue=today, due=+30d) +
  status + notes. After create, redirects to /invoices/[id] for adding
  items.
- /invoices/[id] detail: header strip with status, dates, customer name;
  print/edit/delete actions; items editor card; subtotal/VAT/total card;
  notes card.
- InvoiceItemsEditor: rows are clickable to edit, X button to delete.
  ItemFormSheet for add/edit (description + qty + unitPrice + VAT %).

Print is just window.print() for now — relies on browser dialog. Detail
page deliberately uses tabular-nums for amounts.

src/app/(dashboard)/invoices/[id]/components/header-actions.tsx

@@ -0,0 +1,95 @@
+"use client";
+
+import { useState, useTransition } from "react";
+import { useRouter } from "next/navigation";
+import { Loader2, Pencil, Printer, Trash2 } from "lucide-react";
+import { toast } from "sonner";
+
+import { Button } from "@/components/ui/button";
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from "@/components/ui/dialog";
+import { deleteInvoiceAction } from "@/lib/appwrite/invoice-actions";
+
+import { InvoiceFormSheet } from "../../components/invoice-form-sheet";
+import type { Customer, InvoiceRow } from "../../components/types";
+
+type Props = { invoice: InvoiceRow; customers: Customer[] };
+
+export function InvoiceHeaderActions({ invoice, customers }: Props) {
+  const router = useRouter();
+  const [editOpen, setEditOpen] = useState(false);
+  const [deleting, setDeleting] = useState(false);
+  const [busy, startTransition] = useTransition();
+
+  const handleDelete = () => {
+    startTransition(async () => {
+      const fd = new FormData();
+      fd.set("id", invoice.id);
+      const result = await deleteInvoiceAction(fd);
+      if (result.ok) {
+        toast.success("Fatura silindi.");
+        router.push("/invoices");
+      } else {
+        toast.error(result.error ?? "Silme başarısız.");
+        setDeleting(false);
+      }
+    });
+  };
+
+  return (
+    <>
+      <div className="flex flex-wrap gap-2">
+        <Button variant="outline" size="sm" onClick={() => window.print()}>
+          <Printer className="size-3.5" />
+          Yazdır
+        </Button>
+        <Button variant="outline" size="sm" onClick={() => setEditOpen(true)}>
+          <Pencil className="size-3.5" />
+          Düzenle
+        </Button>
+        <Button
+          variant="ghost"
+          size="sm"
+          className="text-destructive hover:text-destructive"
+          onClick={() => setDeleting(true)}
+        >
+          <Trash2 className="size-3.5" />
+          Sil
+        </Button>
+      </div>
+
+      <InvoiceFormSheet
+        open={editOpen}
+        onOpenChange={setEditOpen}
+        invoice={invoice}
+        customers={customers}
+      />
+
+      <Dialog open={deleting} onOpenChange={setDeleting}>
+        <DialogContent>
+          <DialogHeader>
+            <DialogTitle>Faturayı sil</DialogTitle>
+            <DialogDescription>
+              <strong>{invoice.number}</strong> ve tüm kalemleri silinecek. Bu işlem geri alınamaz.
+            </DialogDescription>
+          </DialogHeader>
+          <DialogFooter>
+            <Button variant="outline" onClick={() => setDeleting(false)} disabled={busy}>
+              Vazgeç
+            </Button>
+            <Button variant="destructive" onClick={handleDelete} disabled={busy}>
+              {busy ? <Loader2 className="size-4 animate-spin" /> : <Trash2 className="size-4" />}
+              Sil
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
+    </>
+  );
+}