feat(hooks): add Unity Git Hooks integration and runHookGroups

Built-in support for Unity Git Hooks (com.frostebite.unitygithooks):
- Auto-detect UPM package in Packages/manifest.json
- Run init-unity-lefthook.js before hook installation
- Set CI-friendly env vars (disable background project mode)

New gitHooksRunBeforeBuild input runs specific lefthook groups before
the Unity build, allowing CI to trigger pre-commit or pre-push checks
that normally only fire on git events.

35 unit tests covering detection, init, CI env, group execution, and
failure handling.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/model/build-parameters.ts

@@ -118,6 +118,7 @@ class BuildParameters {
   public lfsStoragePaths!: string;
   public gitHooksEnabled!: boolean;
   public gitHooksSkipList!: string;
+  public gitHooksRunBeforeBuild!: string;
   public providerExecutable!: string;
 
   public static shouldUseRetainedWorkspaceMode(buildParameters: BuildParameters) {
@@ -267,6 +268,7 @@ class BuildParameters {
       lfsStoragePaths: Input.lfsStoragePaths,
       gitHooksEnabled: Input.gitHooksEnabled,
       gitHooksSkipList: Input.gitHooksSkipList,
+      gitHooksRunBeforeBuild: Input.gitHooksRunBeforeBuild,
       providerExecutable: Input.providerExecutable,
     };
   }