iEduPortal Stage 10 - REST API authentication

POST /api/v1/auth/login.php with JSON:
{"account_type":"parent","username":"Parent1","password":"Parent1"}

Successful response returns a short-lived Bearer access token.
Use it with:
Authorization: Bearer <token>

GET /api/v1/me/

This stage does not change the database schema. It uses the existing authentication layer, including automatic legacy plaintext-to-hash migration.
