Add issue/cancel lifecycle, GST derivation and integer-paise totals

issue_invoice allocates the number, freezes vendor and bank details and
stores server-computed totals in one transaction. Issued invoices are
cancelled, not deleted. Tax heads derive from supplier state and place of
supply (a disagreeing choice is rejected); unregistered suppliers issue a
plain Invoice. Adds GSTIN checksum validation, canonical India Compliance
state list, server-side drafts, series validation, relative and
magic-byte-checked asset paths, and GST settings. PDF re-exports use the
frozen vendor snapshot.

src/views/InvoiceHistory.tsx

@@ -3,6 +3,7 @@ import {
   Button,
   InlineLoading,
   InlineNotification,
+  Modal,
   Table,
   TableBody,
   TableCell,
@@ -10,9 +11,10 @@ import {
   TableHead,
   TableHeader,
   TableRow,
+  Tag,
+  TextInput,
 } from "@carbon/react";
-import { Download, TrashCan } from "@carbon/icons-react";
-import { confirm } from "@tauri-apps/plugin-dialog";
+import { Download, Close } from "@carbon/icons-react";
 import { api } from "../lib/api";
 import { formatAmount, formatDate } from "../lib/format";
 import { exportInvoicePdf } from "../lib/pdf";
@@ -23,6 +25,8 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
   const [busyId, setBusyId] = useState<number | null>(null);
+  const [cancelTarget, setCancelTarget] = useState<InvoiceSummary | null>(null);
+  const [reason, setReason] = useState("");
 
   const load = async () => {
     try {
@@ -52,16 +56,15 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
     }
   };
 
-  const onDelete = async (row: InvoiceSummary) => {
-    const ok = await confirm(`Delete invoice ${row.number}? This cannot be undone.`, {
-      title: "Delete invoice",
-      kind: "warning",
-    });
-    if (!ok) return;
+  const onCancel = async () => {
+    if (!cancelTarget) return;
     try {
-      await api.deleteInvoice(row.id);
+      await api.cancelInvoice(cancelTarget.id, reason);
+      setCancelTarget(null);
+      setReason("");
       await load();
     } catch (e) {
+      setCancelTarget(null);
       setError(String(e));
     }
   };
@@ -99,7 +102,15 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
                   <TableCell>{formatDate(row.invoiceDate)}</TableCell>
                   <TableCell>{row.clientName || "—"}</TableCell>
                   <TableCell>₹{formatAmount(row.total)}</TableCell>
-                  <TableCell>{row.status}</TableCell>
+                  <TableCell>
+                    {row.status === "cancelled" ? (
+                      <Tag type="red" size="sm">
+                        Cancelled
+                      </Tag>
+                    ) : (
+                      row.status
+                    )}
+                  </TableCell>
                   <TableCell>
                     <div className="voiced-header-action">
                       <Button
@@ -111,14 +122,19 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
                       >
                         {busyId === row.id ? "Exporting…" : "PDF"}
                       </Button>
-                      <Button
-                        kind="ghost"
-                        size="sm"
-                        renderIcon={TrashCan}
-                        onClick={() => onDelete(row)}
-                      >
-                        Delete
-                      </Button>
+                      {row.status === "issued" ? (
+                        <Button
+                          kind="ghost"
+                          size="sm"
+                          renderIcon={Close}
+                          onClick={() => {
+                            setReason("");
+                            setCancelTarget(row);
+                          }}
+                        >
+                          Cancel
+                        </Button>
+                      ) : null}
                     </div>
                   </TableCell>
                 </TableRow>
@@ -127,6 +143,26 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
           </Table>
         </TableContainer>
       )}
+
+      <Modal
+        open={cancelTarget !== null}
+        danger
+        modalHeading={`Cancel invoice ${cancelTarget?.number ?? ""}?`}
+        primaryButtonText="Cancel invoice"
+        secondaryButtonText="Keep invoice"
+        onRequestClose={() => setCancelTarget(null)}
+        onRequestSubmit={onCancel}
+      >
+        <p style={{ marginBottom: "1rem" }}>
+          The invoice stays in the list as cancelled and its number is not reused.
+        </p>
+        <TextInput
+          id="cancelReason"
+          labelText="Reason (optional)"
+          value={reason}
+          onChange={(e) => setReason(e.target.value)}
+        />
+      </Modal>
     </div>
   );
 }