Refactor JWT config and enhance security, improve file download, and fix refresh token cleanup

- Restricted public auth endpoints to only /login and /register in SecurityConfig
- Added contentLength header and improved error response in FileController download API
- Refactored JwtService to load secret key and expiration from application properties
- Improved signing key handling using Base64 decoding
- Updated RefreshTokenRepository with @Transactional @Modifying delete query
- Ensured proper refresh token cleanup with flush() in RefreshTokenService
- Annotated refresh token methods with @Transactional for consistency

src/main/java/com/skycrate/backend/skycrateBackend/config/SecurityConfig.java

@@ -29,7 +29,7 @@ public class SecurityConfig {
                 .sessionManagement(session -> session.sessionCreationPolicy(SessionCreationPolicy.STATELESS))
                 .authenticationProvider(authenticationProvider)
                 .authorizeHttpRequests(auth -> auth
-                        .requestMatchers("/api/auth/**", "/actuator/**").permitAll()
+                        .requestMatchers("/api/auth/login", "/api/auth/register", "/actuator/**").permitAll()
                         .requestMatchers(HttpMethod.GET, "/public/**").permitAll()
                         .anyRequest().authenticated()
                 )