Build a multi-panel dashboard with parallel routes instead of client-side tab state

<context>
Dashboard panels needed, and roughly what each one shows: revenue chart (last 30 days), recent activity feed, team member list
Independent navigation requirements — can panels change without a full page reload, do they need their own URLs: The activity feed panel should support its own filter state in the URL; the others don't need deep-linking
</context>

<task>
Structure this dashboard using parallel routes (the @folder convention) inside a shared layout.tsx, with one slot per independent panel, instead of a single page component that fetches everything and manages which panel is "active" with client-side state.
</task>

<requirements>
- Create one @slotName folder per panel under the layout, each with its own page.tsx that fetches only that panel's data.
- Give each slot its own loading.tsx so a slow panel shows its own skeleton and streams in independently — a slow analytics query should never block the activity feed panel from rendering.
- Give each slot its own error.tsx so one panel's fetch failure shows an inline error in that panel only, not a full-page crash.
- Add a default.tsx in each slot that returns null (or a sensible fallback) for the case where a hard navigation/refresh doesn't match that slot's most specific route — without it, Next.js 404s the whole layout on refresh for any slot that doesn't have a matching segment.
- The layout.tsx receives all slots as props (children plus each named slot) and arranges them in the grid/panel layout — it does not itself fetch data.
</requirements>

<output_format>
The folder structure (as a tree), the layout.tsx showing how slots are composed, and one paragraph confirming what happens on a hard refresh when only one slot's URL segment is present.
</output_format>