feat: add RecentCampaigns dashboard component

[AbdulmujibOladayo]

Adds the RecentCampaigns dashboard widget requested in issue #73.

• Creates src/components/dashboard/RecentCampaigns.jsx
• Dispatches fetchRecentCampaigns (already wired in dashboardThunks + dashboardSlice) on mount
• Renders up to 4 campaigns as interactive cards in a 2-column grid
• Each card shows: title, colour-coded status badge, raised/goal amounts, progress bar, and creation date
• Cards link to /campaigns/:id
• Header contains a Create New Campaign button linking to /campaigns/create and a View All link
• Empty state includes a CTA to create the first campaign
• Skeleton cards shown during loading (matches existing dashboard skeleton style)

closes #73

[ayshadogo]

LGTM