Separate NeoGradle release clean and build phases

[SkyBlade1978]

Summary

Repairs the shared Mineralogy release dispatcher after the NeoForge 26.2 release build failed during NeoGradle setup.

The immutable-build job constructed clean and all build tasks in one Gradle invocation. On NeoGradle 7.1 this allowed clean to remove the expanded patch bundle after the task graph had captured it, causing neoFormSetup to fail because patches.lzma no longer existed.

This change:

• runs clean in its own Gradle invocation
• runs tests, build, Javadocs, dependency verification, artifact audit and checksums in a second invocation
• reuses the exact same OreSpawn mirror, toolchain and Gradle arguments for both phases
• adds a workflow contract test that rejects the combined invocation

Evidence

• failed release run: https://github.com/MinecraftModDevelopmentMods/MinecraftMineralogy/actions/runs/34618684435
• no immutable artifact, tag, Maven upload, CurseForge file or GitHub Release was created by the failed run
• focused WorkflowContractTest passes locally
• the equivalent split flow passed locally and in PR Port Mineralogy 6.1.2 to NeoForge 26.2 #172's CodeQL and branch CI jobs

This is release tooling only; it changes no Mineralogy product source or artifact contents.