refine .env URLs

[YoungjaeKim]

AS-IS

1. API

BASE_URL=http://localhost:3000 # default: http://localhost:3000
# APP_PORT=4000 # default: 4000

2. WEB

NEXT_PUBLIC_API_BASE_URL=http://localhost:4000
API_BASE_URL=http://127.0.0.1:3000
NEXT_PUBLIC_MAX_DAYS=90

TO-BE

Objective; (1) clearly define which variable is for API backend or WEB frontend. (2) Remove NEXT_ prefix because our user doesn't consider what NEXT is.

1. API

WEB_BASE_URL=http://localhost:3000
# API_BASE_PORT=4000 # default: 4000

2. WEB

API_BASE_URL=http://localhost:4000
WEB_BASE_URL=http://127.0.0.1:3000
QUERY_MAX_TIMESPAN=90

This could break user experience because environment variables should be changed.

Additional information

It is related to issue #232