feat(ui): add skeleton loading states to CampaignDashboard

[marvs8]

Summary

Replaces the plain spinner in CampaignDashboard with a structured Skeleton layout that mirrors the real content (header row, meta grid, progress bar, steps list), consistent with the rest of the app.

Changes

• CampaignDashboard.tsx: import Skeleton from ../UI/Skeleton; replace spinner div with a skeleton layout wrapped in a container with aria-label='Loading campaign'
• CampaignDashboard.test.tsx: update loading state assertion from getByRole('status') to getByLabelText('Loading campaign')

Testing

• Loading state test passes with the new skeleton assertion
• 5 pre-existing failures (progressPercent.toFixed crash due to missing mock field) were already failing on main before this PR — no regressions introduced

Closes #1211

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