fix(ux): popover collision padding, PWA manifest, webhook toasts, portal toast, dashboard error boundary, GDPR poll backoff, empty-state CTA

Grab-bag of UX gaps from audit-pass-#2 + #3. Each one is a small,
focused fix; bundled because they touch different surfaces.

- Popover: collisionPadding={16} + responsive
  w-[min(calc(100vw-2rem),18rem)] so popovers stop clipping past the
  viewport on iPhone 12 portrait.
- public/manifest.json (was missing) + manifest reference in
  layout.tsx — PWA installability now works; icons (192/512/512-
  maskable) were already present.
- Admin webhooks page: 4 silent `// ignore` catches in load/delete/
  toggle/regenerate replaced with toast.error / toast.success. Users
  no longer see a stale list with no feedback when an op fails.
- Portal document-download button: blocking alert() → toast.error().
- src/app/(dashboard)/error.tsx: branded error boundary with retry +
  back-to-dashboard, replacing Next.js's default uncaught-error UI.
- GDPR export modal: refetchInterval was a flat 5s while the modal was
  open. Switched to a function that only polls (every 15s) when a job
  is actually pending/building; settled exports stop polling entirely.
- client-yachts-tab empty state gains a CTA wired to the existing
  Add-yacht dialog, instead of just saying "No yachts".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/(dashboard)/[portSlug]/admin/webhooks/page.tsx

@@ -1,6 +1,7 @@
 'use client';
 
 import { useCallback, useEffect, useState } from 'react';
+import { toast } from 'sonner';
 import { Button } from '@/components/ui/button';
 import { PageHeader } from '@/components/shared/page-header';
 import { Badge } from '@/components/ui/badge';
@@ -47,8 +48,8 @@ export default function WebhooksPage() {
     try {
       const result = await apiFetch<{ data: Webhook[] }>('/api/v1/admin/webhooks');
       setWebhooks(result.data);
-    } catch {
-      // ignore
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : 'Failed to load webhooks');
     } finally {
       setLoading(false);
     }
@@ -63,9 +64,10 @@ export default function WebhooksPage() {
     try {
       await apiFetch(`/api/v1/admin/webhooks/${deleteTarget.id}`, { method: 'DELETE' });
       setDeleteTarget(null);
+      toast.success('Webhook deleted');
       void loadWebhooks();
-    } catch {
-      // ignore
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : 'Failed to delete webhook');
     }
   }
 
@@ -78,8 +80,8 @@ export default function WebhooksPage() {
       );
       setNewSecret({ webhookId, secret: result.data.secret, masked: result.data.secretMasked });
       void loadWebhooks();
-    } catch {
-      // ignore
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : 'Failed to regenerate secret');
     } finally {
       setRegenerating(null);
     }
@@ -91,9 +93,10 @@ export default function WebhooksPage() {
         method: 'PATCH',
         body: { isActive: !webhook.isActive },
       });
+      toast.success(webhook.isActive ? 'Webhook disabled' : 'Webhook enabled');
       void loadWebhooks();
-    } catch {
-      // ignore
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : 'Failed to toggle webhook');
     }
   }