feat: add JWT auth and inventory dependencies

Add PyJWT, bcrypt, openpyxl to requirements.
Add JWT_SECRET, JWT_ACCESS_EXPIRES, JWT_REFRESH_EXPIRES to config.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

config.py

@@ -15,6 +15,11 @@ SQLITE_PATH = os.path.join(
     "vehicle_database", "vehicle_database.db"
 )
 
+# JWT Authentication
+JWT_SECRET = os.environ.get("JWT_SECRET", "nexus-saas-secret-change-in-prod-2026")
+JWT_ACCESS_EXPIRES = 900       # 15 minutes
+JWT_REFRESH_EXPIRES = 2592000  # 30 days
+
 # Application identity
 APP_NAME = "NEXUS AUTOPARTS"
 APP_SLOGAN = "Tu conexión directa con las partes que necesitas"