feat: big cleanup and refactor

[apotdevin]

Summary

• Migrated frontend from Next.js to Vite + React Router — replaced Next.js file-based routing, SSR, and _app.tsx/_document.tsx with a Vite-built SPA using React Router, a new App.tsx root component, and @nestjs/serve-static for serving the client bundle
• Replaced WebSocket transport with Server-Sent Events (SSE) — removed the WebSocket gateway (ws.gateway.ts) and SocketContext in favor of a new NestJS SSE controller and SseContext on the client
• Removed deprecated integrations and features — removed LN Markets integration, BOS rebalancing flow, base/Thunder points system, accounting report tool, leaderboard, and night theme
• Major dependency upgrades — Node 18 → 24, NestJS 10 → 11, Express 4 → 5, Tailwind CSS v4 with Vite plugin, @nestjs/serve-static v5, migrated ESLint to flat config
• UI component modernization — migrated select, slider, and modal components to shadcn/ui, switched to Lucide icons, replaced numeral with native formatting, added new SVG progress bar and toast library
• Added Docker Hub CI — new GitHub Action to build and push multi-arch (amd64/arm64) images on version tags
• Dockerfile modernized — Node 24 alpine base, Vite build output, non-root user, removed Next.js telemetry and artifacts
• Dropped linux/arm/v7 from Docker builds — multi-arch images now target only amd64 and arm64

Breaking Changes

• Removed LN Markets integration
• Removed BOS rebalancing flow
• Removed accounting report tool
• Removed base/Thunder points system
• Removed night theme
• Dropped linux/arm/v7 Docker image support