fix(orchestrator): use http.extraHeader for secure git authentication

Replace token-in-URL pattern with http.extraHeader for git clone and LFS
operations. The token no longer appears in clone URLs, git remote config,
or process command lines.

Add gitAuthMode input (default: 'header', legacy: 'url') so users can
fall back to the old behavior if needed.

Closes #785

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

src/model/orchestrator/options/orchestrator-options.ts

@@ -138,6 +138,10 @@ class OrchestratorOptions {
     return provider || 'local';
   }
 
+  static get gitAuthMode(): string {
+    return OrchestratorOptions.getInput('gitAuthMode') || 'header';
+  }
+
   static get containerCpu(): string {
     return OrchestratorOptions.getInput('containerCpu') || `1024`;
   }