feat: implement UI matrix for assigning Keto permissions to hub operator roles

[CodeBySayak]

Overview

This PR introduces a UI for Hub Operators to visually assign permissions to roles using a matrix-based interface. It includes a standalone web app (hub-permissions) integrated with Keto (Zanzibar-style) permission tuples.

Key Features

• Permission Matrix UI
  Responsive grid mapping actions (e.g., dfspManage, settlementView) to roles (Admin, Manager, Operator, Viewer)

• Keto Tuple Integration
  Aligns with Zanzibar tuple structure:
  namespace → object → relation → subject

• Live API Preview Panel
  Displays relevant REST endpoints dynamically on permission hover

• Toast Notifications
  Shows generated JSON/Keto payloads on assignment (POST) and removal (DELETE)

• Mock API Server
  Lightweight Express server (server.js) supporting:

  • GET /api/metadata
  • POST /api/tuples
  • DELETE /api/tuples

Design

• Dark mode UI with glassmorphism styling
• Inter font and smooth animated checkbox interactions

Type of Change

• New feature
• Bug fix
• Refactoring

Testing

• Verified locally using node server.js
• Checkbox interactions correctly trigger:
  • POST on assign
  • DELETE on unassign
• Hover states update the API preview panel without layout shifts

fixes #4409

[CLAassistant]

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