Add toasts, Settings tabs, Clients page and item presets (Phase E1)

- Global Carbon toast stack replaces scattered inline notices; errors persist until closed.
- Settings is split into eight tabs with one Save and a remembered last tab; Numbering embeds the series settings.
- New Clients page with a DataTable, shared add/edit modal, structured addresses, GST category (informational), per-client notes and payment terms. The composed address string is kept for back-compat. Deleting a client warns about invoice count; issued invoices keep their own snapshot.
- Migration M7 adds the client columns and item_presets; existing clients with a GSTIN are backfilled to registered_regular.
- New invoice form: client ComboBox with type-ahead and inline create, client defaults applied on selection, and an Add from preset control.
- Rust tests for M7 (fresh and v6 upgrade), client validation and CRUD, presets CRUD; vitest for the toast store and new helpers.

PDF output and fingerprint goldens are unchanged. The new UI has not been run in a webview yet.

src/views/SeriesSettings.tsx

@@ -4,7 +4,6 @@ import {
   Column,
   Grid,
   InlineLoading,
-  InlineNotification,
   NumberInput,
   Table,
   TableBody,
@@ -19,8 +18,17 @@ import {
 import { confirm } from "@tauri-apps/plugin-dialog";
 import { api } from "../lib/api";
 import type { InvoiceSeries } from "../lib/types";
+import { useToast } from "../components/ToastProvider";
 
-export default function SeriesSettings({ active: visible }: { active: boolean }) {
+export default function SeriesSettings({
+  active: visible,
+  embedded = false,
+}: {
+  active: boolean;
+  /** Rendered inside Settings: no page wrapper or title. */
+  embedded?: boolean;
+}) {
+  const toast = useToast();
   const [active, setActive] = useState<InvoiceSeries | null>(null);
   const [all, setAll] = useState<InvoiceSeries[]>([]);
   const [loading, setLoading] = useState(true);
@@ -28,8 +36,6 @@ export default function SeriesSettings({ active: visible }: { active: boolean })
   const [prefix, setPrefix] = useState(`INV/${new Date().getFullYear()}-`);
   const [padding, setPadding] = useState(3);
   const [busy, setBusy] = useState(false);
-  const [error, setError] = useState<string | null>(null);
-  const [notice, setNotice] = useState<string | null>(null);
 
   const seeded = useRef(false);
 
@@ -44,9 +50,8 @@ export default function SeriesSettings({ active: visible }: { active: boolean })
         setPadding(current.padding);
         seeded.current = true;
       }
-      setError(null);
     } catch (e) {
-      setError(String(e));
+      toast.error("Could not load series", String(e));
     } finally {
       setLoading(false);
     }
@@ -65,47 +70,34 @@ export default function SeriesSettings({ active: visible }: { active: boolean })
     );
     if (!ok) return;
     setBusy(true);
-    setError(null);
-    setNotice(null);
     try {
       const created = await api.startNewSeries(prefix, padding);
-      setNotice(`New series started. Next invoice: ${created.nextInvoiceNumber}`);
+      toast.success("New series started", `Next invoice: ${created.nextInvoiceNumber}`);
       await load();
     } catch (e) {
-      setError(String(e));
+      toast.error("Could not start a new series", String(e));
     } finally {
       setBusy(false);
     }
   };
 
+  const pageClass = embedded ? undefined : "voiced-page";
+
   if (loading) {
     return (
-      <div className="voiced-page">
+      <div className={pageClass}>
         <InlineLoading description="Loading series" />
       </div>
     );
   }
 
   return (
-    <div className="voiced-page">
-      <h1 className="voiced-page__title">Invoice series</h1>
-      <p className="voiced-page__subtitle">
+    <div className={pageClass}>
+      {embedded ? null : <h1 className="voiced-page__title">Invoice series</h1>}
+      <p className={embedded ? "voiced-muted" : "voiced-page__subtitle"}>
         The active series drives the automatic invoice numbers. Start a new series to reset the counter.
       </p>
 
-      {error ? (
-        <InlineNotification kind="error" lowContrast title="Something went wrong" subtitle={error} />
-      ) : null}
-      {notice ? (
-        <InlineNotification
-          kind="success"
-          lowContrast
-          title="Done"
-          subtitle={notice}
-          onCloseButtonClick={() => setNotice(null)}
-        />
-      ) : null}
-
       <Grid narrow style={{ marginBottom: "2rem" }}>
         <Column sm={4} md={4} lg={6}>
           <TextInput