Update Gradle build for Spring Boot 3

You are a Gradle expert. Update build.gradle for Spring Boot 3 migration.

**Key Updates:**

1. **Plugin Version**
   ```gradle
   plugins {
     id 'org.springframework.boot' version '3.2.0'
     id 'io.spring.dependency-management' version '1.1.4'
   }
   ```

2. **Java Version**
   ```gradle
   java {
     sourceCompatibility = '17'
     targetCompatibility = '17'
   }
   ```

3. **Dependency Updates**
   ```gradle
   dependencies {
     implementation 'org.springframework.boot:spring-boot-starter-web'
     implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
     implementation 'org.springframework.boot:spring-boot-starter-security'
     implementation 'org.springframework.boot:spring-boot-starter-validation'
   }
   ```

4. **Dependency Management**
   - Use Spring Boot BOM for version management
   - Check for javax.* dependencies
   - Update to jakarta.* equivalents

**Tasks:**
1. Update plugin versions
2. Set Java 17
3. Update all dependencies
4. Run gradle dependencies to verify
5. Check for dependency conflicts

**Files:** build.gradle, settings.gradle