Add SKIP_GPS_VALIDATION feature for attendance and visit services

- Introduced SKIP_GPS_VALIDATION environment variable to control GPS validation during check-ins and check-outs.
- Updated loadEnv function to parse SKIP_GPS_VALIDATION and enforce its rules based on NODE_ENV.
- Enhanced attendance and visit services to utilize the new configuration, allowing GPS validation to be skipped in development environments.
- Added unit tests to verify the behavior of SKIP_GPS_VALIDATION in various scenarios, ensuring proper handling in both production and development contexts.
- Updated check-in verification logic to respect the SKIP_GPS_VALIDATION option, improving flexibility in location checks.

.env.example

@@ -23,3 +23,7 @@ BCRYPT_SALT_ROUNDS=10
 # OpenAPI UI at /docs (default: on unless NODE_ENV=production)
 # SWAGGER_ENABLED=true
 # SWAGGER_ENABLED=false
+
+# Debug only. Skip GPS radius/location checks on check-in and check-out.
+# Rejected when NODE_ENV=production.
+# SKIP_GPS_VALIDATION=true