P15c: client UI for shared campaigns + publishing characters

- src/lib/cloud/campaigns.ts wraps the campaign/character API.
- Settings "Shared campaigns (cloud)" panel (signed-in only): publish a local
  campaign → get an invite code; join a campaign by code; publish a local character
  to a campaign (stays yours, re-publish to sync); owners "View party" to read all
  published characters (read-all, per the View+suggest model).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/features/settings/SettingsPage.tsx

@@ -6,6 +6,7 @@ import { pickTextFile } from '@/lib/io/file';
 import { seedSampleCampaign } from '@/lib/sample';
 import { cloudUsername, register as cloudRegister, login as cloudLogin, logout as cloudLogout, pushBackup, pullBackup, CloudError } from '@/lib/cloud/client';
 import { AssistantSettings } from './AssistantSettings';
+import { CloudCampaigns } from './CloudCampaigns';
 import { Page, PageHeader } from '@/components/ui/Page';
 import { Button } from '@/components/ui/Button';
 import { Modal } from '@/components/ui/Modal';
@@ -71,6 +72,8 @@ export function SettingsPage() {
 
       <CloudSync />
 
+      <CloudCampaigns />
+
       <section className="rounded-lg border border-line bg-panel p-4">
         <h2 className="mb-2 text-xs font-semibold uppercase tracking-wide text-muted">Data sources &amp; licenses</h2>
         <ul className="space-y-1 text-sm text-muted">