feat(walkthrough): add Getting Started tour with first-run invite

Bespoke spotlight walkthrough (no new deps) that guides new users through the
main features. A version-stamped invite bubble offers the tour to new users and
re-offers it once to existing users after an upgrade; restartable from Settings.

- Multi-hole SVG-mask overlay keeps a ringed control and any open modal lit
- Steps: scan, scan history, inventory, nodes, edit, text/zone, grouping,
  style, imports, and a closing recap with a GitHub link
- Scan/history/inventory/import steps inject demo data (no backend calls) and
  are filtered out in standalone, which ends on a full-mode recap
- Persisted invite state via localStorage (utils/walkthrough.ts), live tour
  state via zustand (stores/walkthroughStore.ts)

ha-relevant: maybe

frontend/src/walkthrough/demoTourData.ts

@@ -0,0 +1,65 @@
+import type { ScanRun } from '@/components/modals/ScanHistoryModal'
+import type { PendingDevice } from '@/components/modals/PendingDeviceModal'
+
+/**
+ * Canned data injected into the real modals during the tour, so the demo steps
+ * look alive on a fresh install without hitting the backend. Never persisted.
+ */
+export const DEMO_SCAN_RUNS: ScanRun[] = [
+  {
+    id: 'tour-scan-running',
+    status: 'running',
+    kind: 'ip',
+    ranges: ['192.168.1.0/24'],
+    devices_found: 12,
+    // 8s ago so the live "Duration" reads a realistic elapsed time.
+    started_at: new Date(Date.now() - 8000).toISOString(),
+    finished_at: null,
+    error: null,
+  },
+  {
+    id: 'tour-scan-done',
+    status: 'done',
+    kind: 'ip',
+    ranges: ['192.168.1.0/24'],
+    devices_found: 9,
+    started_at: new Date(Date.now() - 3600_000).toISOString(),
+    finished_at: new Date(Date.now() - 3560_000).toISOString(),
+    error: null,
+  },
+]
+
+export const DEMO_PENDING_DEVICES: PendingDevice[] = [
+  {
+    id: 'tour-dev-1',
+    ip: '192.168.1.20',
+    mac: 'AA:BB:CC:DD:EE:20',
+    hostname: 'synology-nas',
+    os: 'DSM 7.2',
+    services: [{ port: 5000, protocol: 'tcp', service_name: 'Synology DSM', category: 'nas' }],
+    suggested_type: 'nas',
+    status: 'pending',
+    discovery_source: 'arp',
+    friendly_name: 'Synology NAS',
+    vendor: 'Synology',
+    model: 'DS920+',
+    discovered_at: new Date(Date.now() - 120_000).toISOString(),
+    canvas_count: 0,
+  },
+  {
+    id: 'tour-dev-2',
+    ip: '192.168.1.30',
+    mac: 'AA:BB:CC:DD:EE:30',
+    hostname: 'pi-hole',
+    os: null,
+    services: [{ port: 80, protocol: 'tcp', service_name: 'Pi-hole', category: 'network' }],
+    suggested_type: 'generic',
+    status: 'pending',
+    discovery_source: 'arp',
+    friendly_name: 'Pi-hole',
+    vendor: 'Raspberry Pi',
+    model: null,
+    discovered_at: new Date(Date.now() - 90_000).toISOString(),
+    canvas_count: 0,
+  },
+]