Analytics Dashboard

Build an analytics dashboard with the following features:

**Layout:**
- Left sidebar with navigation: Overview, Revenue, Users, Events, Settings
- Top bar: date range picker (Last 7 days / 30 days / 90 days / Custom), export CSV button, user avatar
- Responsive: sidebar collapses to hamburger on mobile

**Overview Page:**
- 4 KPI cards at the top: Total Revenue, Active Users, Signups This Period, Conversion Rate — each with the current number, delta vs previous period (green/red), and a sparkline
- Large line chart showing revenue over time (toggle daily/weekly/monthly)
- Two side-by-side charts: bar chart of top referral sources, donut chart of user plan mix (Free/Pro/Team)
- Recent activity table: last 20 events with user, event type, timestamp

**Filters:**
- Every chart respects the global date range picker
- Optional segment filter: plan, country, device

**Data:**
- Pull from Supabase tables: users, events, subscriptions, revenue_daily
- All queries use a date range parameter
- Empty states: "No data for this range — try a wider date window"

**Design:**
- Clean light theme with neutral greys and a single accent colour
- Use Recharts for all charts
- Card-based layout with subtle borders
- Loading skeletons for every card/chart
- Responsive on mobile

Store everything in Supabase. Use Row Level Security so each user only sees their own data.