Show only campaigns on the home page, not groups and pledges

The home page is the primary browse surface for campaigns and reads best
when it stays focused on them. Groups and Pledges each have their own
dedicated browse pages (/groups, /pledges), so surfacing all three on /
duplicated those experiences and diluted the page.

Drop the GroupsDiscoverySection and PledgesDiscoverySection from the home
page, leaving only CampaignsDiscoverySection. The shared discovery
components and the dedicated pages that consume them are untouched.

Regression-of: 7ccff2fb

src/pages/CampaignsPage.tsx

@@ -6,24 +6,23 @@ import { ArrowRight, PlusCircle } from 'lucide-react';
 import { Button } from '@/components/ui/button';
 import { HeroLightningMap } from '@/components/HeroLightningMap';
 import { CampaignsDiscoverySection } from '@/components/discovery/CampaignsDiscoverySection';
-import { GroupsDiscoverySection } from '@/components/discovery/GroupsDiscoverySection';
-import { PledgesDiscoverySection } from '@/components/discovery/PledgesDiscoverySection';
 import { useAppContext } from '@/hooks/useAppContext';
 import { useCurrentUser } from '@/hooks/useCurrentUser';
 
 /**
  * Home page (`/`).
  *
- * Hero on top, then the three discovery sections back-to-back —
- * Campaigns, Groups, Pledges — each with the same title, tagline,
- * and search/sort/country toolbar as its dedicated page. Filter
- * state is purely local here (`filterPersistence="local"`):
- * persisting three sets of `?q=&sort=&country=` would either
- * collide (three sections want `?q=`) or pollute the URL with
- * prefixed variants on every keystroke. Refreshing `/` always
- * lands on the curated idle view, which matches what we want
- * anyway. Users who want shareable / persistent filters go to
- * `/campaigns/all`, `/groups`, or `/pledges`.
+ * Hero on top, then the campaigns discovery section — with the same
+ * title, tagline, and search/sort/country toolbar as the dedicated
+ * `/campaigns/all` page. Filter state is purely local here
+ * (`filterPersistence="local"`): persisting `?q=&sort=&country=`
+ * would pollute the URL on every keystroke, and refreshing `/`
+ * should always land on the curated idle view. Users who want
+ * shareable / persistent filters go to `/campaigns/all`.
+ *
+ * Groups and Pledges have their own dedicated browse pages
+ * (`/groups`, `/pledges`); the home page intentionally surfaces
+ * only campaigns so it stays focused and scannable.
  *
  * The home page intentionally omits the moderator-only Hidden
  * collapsibles and per-viewer "My X" shelves — those live on the
@@ -48,8 +47,6 @@ export function CampaignsPage() {
         id="discover"
       >
         <CampaignsDiscoverySection filterPersistence="local" />
-        <GroupsDiscoverySection filterPersistence="local" />
-        <PledgesDiscoverySection filterPersistence="local" />
       </div>
     </main>
   );