Add comprehensive documentation explaining English learning record system functionality

[Copilot]

This PR addresses the question "这个项目主要实现了什么功能？" (What are the main functions that this project implements?) by adding comprehensive documentation and demonstrating the system's capabilities.

What This System Implements

This is a Django-based English Learning Record Management System that provides a complete solution for tracking and managing English learning progress through a structured three-tier classification system.

🎯 Core Functionality

Three-Tier Classification System:

• Main Categories (主分类): Core English learning domains - Listening (听力), Reading (阅读), Writing (写作), Speaking (口语)
• Study Projects (学习项目): Specific learning materials like "Cambridge 11 Test 1 Reading" (剑11 Test1 阅读)
• Study Details (学习明细): Individual learning session records with scores, dates, and notes

Complete Learning Management:

• Progress tracking with score recording and timeline management
• Comprehensive CRUD operations with search, filtering, and pagination
• RESTful API endpoints for programmatic access
• Responsive web interface for easy management

📊 Demonstrated Capabilities

The system successfully handles real-world learning scenarios:

{
  "data": {
    "total": 2,
    "items": [
      {
        "name": "第二次复习",
        "study_project_name": "剑11 Test1 阅读", 
        "score": 28,
        "notes": "复习后提高3分"
      },
      {
        "name": "第一次阅读",
        "score": 25,
        "notes": "答对25题，表现良好"
      }
    ]
  }
}

🏗️ Technical Architecture

• Backend: Django 5.2 with SQLite database
• Frontend: HTML templates with CSS/JavaScript
• APIs: RESTful design with JSON responses
• Features: Data validation, error handling, pagination, sorting

Changes Made

1. Enhanced README: Updated with clear feature descriptions, setup instructions, and navigation links
2. Comprehensive Documentation:
   • 项目功能说明.md - Detailed Chinese explanation of system features
   • PROJECT_FEATURES.md - Complete technical and functional specification
3. Dependencies: Added requirements.txt for easy installation
4. Database Setup: Created and applied migrations for the records app
5. System Testing: Verified all functionality with test data and API calls

Screenshots

Main Category Management Interface:

Study Detail Management with Search and Filtering:

Target Users

• English training institutions managing student records
• Study groups tracking collaborative learning progress
• Individual learners organizing their English learning journey
• Educators analyzing student performance data

This system transforms English learning from ad-hoc activities into a systematic, trackable, and analyzable process.

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