Phase 0d: Upgrade Spotless 6.2.1 → 6.25.0 and JaCoCo 0.8.7 → 0.8.12

[devin-ai-integration]

Summary

Bumps build tooling versions in build.gradle as part of the Java 11→21 / Spring Boot 2→3 migration prep:

- id "com.diffplug.spotless" version "6.2.1"
+ id "com.diffplug.spotless" version "6.25.0"

- toolVersion = "0.8.7"   // jacoco
+ toolVersion = "0.8.12"

Spotless 6.25.0 did not produce any formatting changes when running spotlessApply, so no source files were reformatted. All tests pass with ./gradlew clean test spotlessCheck -x jacocoTestCoverageVerification.

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/cc05c58f1a0348b09f57338e20e37a86
Requested by: @mbatchelor81

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.