Upgrade JaCoCo to 0.8.12 for Java 21 support and apply Spring Boot 4 updates

[Copilot]

PR #6592 failed at JaCoCo report generation with "Unsupported class file major version 65". JaCoCo 0.8.8 predates Java 21 support.

Changes

• JaCoCo: 0.8.8 → 0.8.12 (parent pom)
• Spring Boot 4: 4.0.0-M3 → 4.0.0 (GA release)
• Jakarta Servlet: 6.0.0 → 6.1.0
• Compiler target: Java 17 → 21 for spring-boot-4-starter module
• Add explicit spring-jdbc 6.2.0 dependency
• Remove @AutoConfigureBefore(DataSourceAutoConfiguration.class) and DataSourceProperties references (no longer exist in Spring Boot 4)
• Reorganize module-info.java requires ordering
• Clean up configuration metadata (remove redundant type declarations)

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