Upgrade to Grails 8.0.0-M2 / Gradle 9.6.1

[lbwexler]

Summary

Upgrades Toolbox to Grails 8.0.0-M2 (Spring Boot 4.1 / Spring Framework 7) and Gradle 9.6.1, tracking the companion hoist-core change.

Depends on xh/hoist-core#574 — Toolbox needs a Grails-8-capable hoist-core. That PR must merge and publish a 41.0-SNAPSHOT before this branch builds against packaged hoist-core (runHoistInline=false). Until then, build locally with runHoistInline=true.

Key changes

• grailsVersion 7.2.0 → 8.0.0-M2.
• Gradle wrapper 8.14.5 → 9.6.1.
• Adopted the updated hoist-core MCP install snippet (drift marker v1 → v2) — see Upgrade to Grails 8.0.0-M2 / Gradle 9.6.1 hoist-core#574 for the rationale.

Verification

Built and run in composite mode (runHoistInline=true) against the local hoist-core grails-8-upgrade branch:

• ./gradlew clean assemble installHoistCoreTools check — green (WAR builds; MCP launchers regenerate).
• ./gradlew bootRun (H2) — app starts in ~5s on Grails 8.0.0-M2 / Spring Boot 4.1.0 / Spring 7.0.8 / JVM 21; /xh/version returns JSON and /xh/environment returns 401 (auth gating intact).