feat: implement treasury chart area visualization

[2593803287-hue]

Closes #1

Summary

• Implements the dashboard TreasuryChart as a focused Recharts AreaChart with Total Contributions and Loans Outstanding series.
• Uses the requested brand colors (#16a34a and #d97706), USDC tooltip formatting, skeleton loading, empty state CTA, and responsive card styling.
• Supports an optional groupId prop for GET /api/groups/:id/contributions; falls back to clear demo data until the dashboard wires a selected group id.

Verification support

• Adds the minimal repository setup needed for non-interactive validation: Next ESLint config, standard next-env.d.ts, valid next.config.mjs syntax, a missing analytics color fallback, and lazy wallet-kit initialization so SSR build does not crash.
• Keeps this PR focused on issue [Frontend] Implement TreasuryChart component with Recharts area chart #1 while only touching validation blockers required for repository-level checks.

Verification

• npm run type-check
• npm run lint
• npm run build

Note: next build exits successfully. It still reports existing Stellar SDK / sodium-native dynamic require warnings from the Stellar dependency chain.

[2593803287-hue]

Hi maintainers, I submitted this focused implementation for bounty issue #1.

This PR closes #1 and keeps the implementation centered on the TreasuryChart requirement, with repository-level verification included.

Could you please confirm whether any additional bounty-claim step is required, such as a wallet address, bounty platform profile, or claim form?