feat: add revenue chart, empty state, avatar uploader, and notification dropdown

[Nimatstar]

Summary

Implements four frontend components inside rontend/cntr/ as specified in the linked issues.

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[FE-04] Revenue Bar Chart

Files: rontend/cntr/charts/RevenueChart.tsx, RevenueChart.test.tsx

echarts BarChart, Bar, XAxis, YAxis, Tooltip, ResponsiveContainer

• Y-axis and tooltip values formatted as ? using oLocaleString('en-NG')
• Props: data: { month, revenueKobo }[]

[FE-08] Empty State Component

Files: rontend/cntr/EmptyState/EmptyState.tsx, EmptyState.test.tsx

• Props: itle (required), description?, icon?, �ction?: { label, onClick }
• Falls back to lucide-react Inbox icon when none provided
• Action button only renders when �ction prop is present

[FE-11] Profile Avatar Uploader

Files: rontend/cntr/AvatarUploader/AvatarUploader.tsx, AvatarUploader.test.tsx

• Accepts JPEG/PNG only - shows error for other types
• Rejects files > 2MB with error message
• Preview via URL.createObjectURL, revoked on unmount
• Keyboard-accessible trigger with �ria-label

[FE-13] Notification Dropdown

Files: rontend/cntr/NotificationDropdown/NotificationDropdown.tsx, NotificationDropdown.test.tsx

• Bell button toggles dropdown; closes on outside click via useRef + mousedown listener
• Shows last 10 notifications; unread items have �g-blue-50 background + blue dot indicator
• Relative timestamps via Intl.RelativeTimeFormat (no external date library)
• "Mark all read" calls onMarkAllRead prop; "View all" calls onViewAll prop

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closes #983
closes #987
closes #990
closes #992

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