Fix: Pass GitHub token to MCP servers in agent mode

The token was being obtained successfully but not outputted from the prepare step for use in later steps. Added explicit output of the GitHub token and debug logging.

src/entrypoints/prepare.ts

@@ -56,6 +56,7 @@ async function run() {
       mode,
       githubToken,
     });
+    core.setOutput("GITHUB_TOKEN", githubToken);
 
     // MCP config is handled by individual modes (tag/agent) and included in their claude_args output
 

src/modes/agent/index.ts

@@ -41,6 +41,8 @@ export const agentMode: Mode = {
 
   async prepare({ context, githubToken }: ModeOptions): Promise<ModeResult> {
     // Agent mode handles automation events and any event with explicit prompts
+    
+    console.log(`Agent mode: githubToken provided: ${!!githubToken}, length: ${githubToken?.length || 0}`);
 
     // TODO: handle by createPrompt (similar to tag and review modes)
     // Create prompt directory