perf: debounce + AbortController, memo rows, dynamic recharts, image docs

[Teeeyanaa]

Summary

Four mechanical performance and convention fixes across the dashboard.

1. Admin settlements — debounce + AbortController (admin/settlements/page.tsx)

• Added a separate merchantIdInput state the text field binds to, keeping the input immediately responsive while the fetch is gated.
• A debounce effect (400 ms) copies the typed value into filters.merchantId only after the user pauses, eliminating per-keystroke round-trips.
• The fetch effect creates a new AbortController on each run and passes { signal } to Axios. The cleanup calls controller.abort(), cancelling any superseded in-flight request and preventing out-of-order response application.
• As a side-effect, fixes the pre-existing react-hooks/exhaustive-deps ESLint warning by moving fetchSettlements inside the effect.

2. Memoized row components — payments, settlements, webhooks

Extracted React.memo subcomponents for every list page so rows skip re-renders on parent state changes (modal open/close, loading flag) that don't affect row data:

Page	Components added
payments/page.tsx	PaymentTableRow, PaymentMobileCard
settlements/page.tsx	SettlementTableRow, SettlementMobileCard
webhooks/page.tsx	WebhookRow

Callbacks are passed as stable useState setter props so they don't break memo equality.

3. Dynamic recharts — analytics page

• Moved PieChart logic into StatusPieChart.tsx and BarChart logic into VolumeBarChart.tsx.
• Both loaded via next/dynamic(..., { ssr: false }) in analytics/page.tsx.
• Recharts is now code-split into a lazy chunk fetched only when /dashboard/analytics is visited. Merchants who never visit analytics never download it.

4. next/image convention — README

Added an Images section to the Architecture section of README.md documenting next/image as the required pattern for any future merchant logos, avatars, or marketing assets — with usage examples and a note on remotePatterns in next.config.js.

Testing

• npm run lint — no new errors introduced (all pre-existing errors confirmed via git stash before/after comparison)
• No functional behaviour changed on any page; all changes are structural (state shape, component boundaries, import strategy)

closes #203
closes #204
closes #205
closes #206

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