refactor: migrate to unified full-stack monorepo architecture

[Clawue884]

Summary

This pull request introduces a unified full-stack architecture for Door by
combining backend services and frontend delivery into a single Node.js service.

The goal is to provide real-time Pi Network monitoring with a lightweight,
auditable, and easy-to-deploy structure aligned with Pi ecosystem principles.

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Key Features

• Unified Node.js server serving:
  • HTTP static frontend
  • WebSocket real-time stream
• Real-time ledger monitoring (poll-based, read-only)
• Live network metrics broadcast to frontend
• Zero external frontend build dependency (Vue via CDN)
• Simple, auditable, single-service design

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Architecture

• Backend: Node.js + TypeScript
• Realtime: WebSocket
• Frontend: Vue 3 (served directly by backend)
• Pattern: Unified Full-Stack Monorepo (single service)

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Files Added

• src/server.ts – HTTP + WebSocket server
• src/monitor.ts – Ledger polling logic
• src/types.ts – Shared data types
• package.json – Unified service dependencies
• web/index.html – Realtime frontend dashboard

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Motivation

This change prepares Door to evolve from a static analytics dashboard into a
real-time network intelligence tool, while keeping the codebase simple,
transparent, and easy to audit by the Pi community.

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Notes

• Read-only access (no transaction signing)
• No protocol changes
• Safe for public deployment