ENHANCEMENT: Move all hardcoded configuration to environment variables and Flask config system

[Senthil455]

Description

All sensitive configuration values are currently hardcoded in app.py as global variables. This is a security risk and makes deployment across different environments (dev, staging, production) error-prone.

Current Hardcoded Values

• app.py:13 - app.secret_key = "your_secret_key"
• app.py:15 - TEACHER_SUPERKEY = "1"
• app.py:28-32 - Database credentials fallback (postgres / 4321)
• app.py:37-39 - Hardcoded email domains (@student.annauniv.edu, @faculty.annauniv.edu)

Recommended Enhancement

1. Create a proper configuration module using Flask's config system:

   class Config:
       SECRET_KEY = os.environ.get('SECRET_KEY', os.urandom(24).hex())
       TEACHER_SUPERKEY = os.environ.get('TEACHER_SUPERKEY', '')
       DATABASE_URL = os.environ.get('DATABASE_URL', '')
       STUDENT_EMAIL_DOMAIN = os.environ.get('STUDENT_EMAIL_DOMAIN', '@student.annauniv.edu')
       FACULTY_EMAIL_DOMAIN = os.environ.get('FACULTY_EMAIL_DOMAIN', '@faculty.annauniv.edu')
   
   app.config.from_object(Config)

2. Add a .env.example file documenting all required environment variables:

   SECRET_KEY=<generate a random key>
   TEACHER_SUPERKEY=<generate a random key>
   DATABASE_URL=postgresql://user:password@host:port/dbname
   STUDENT_EMAIL_DOMAIN=@student.annauniv.edu
   FACULTY_EMAIL_DOMAIN=@faculty.annauniv.edu
   

3. Recommend using python-dotenv for local development (load .env file automatically)