fix(ci): don't splat empty --commit (PS5.1 drops zero-length args)

PowerShell 5.1 drops a zero-length string when splatting to a native
exe, so an empty $repoCommit shifted flag/value pairing and click saw
the build command as an unexpected positional. Append --commit only
when a commit is set.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/actions/local-ci-build/action.yml

@@ -299,12 +299,14 @@ runs:
         }
 
         # Build argument list for the Python CLI. Long-form kebab-case flags only.
+        # NOTE: never put an empty string in the splatted array — PowerShell
+        # 5.1 drops zero-length args when calling a native exe, which would
+        # shift the flag/value pairing. Add optional args conditionally.
         $pyArgs = @(
             '-m', 'ci_orchestrator', 'job',
             '--job-id',                $jobId,
             '--repo-url',              $repoUrl,
             '--branch',                $repoBranch,
-            '--commit',                $repoCommit,
             '--build-command',         $env:INPUT_BUILD_COMMAND,
             '--guest-artifact-source', $env:INPUT_ARTIFACT_SOURCE,
             '--guest-os',              $resolvedGuestOS,
@@ -312,6 +314,7 @@ runs:
             '--template-path',         $resolvedTemplatePath,
             '--snapshot-name',         $resolvedSnapshotName
         )
+        if ($repoCommit) { $pyArgs += @('--commit', $repoCommit) }
 
         # Submodules and transport default to ON; pass the explicit
         # negative flag when the caller opted out so the Python default