feat: display detailed error messages when prepare step fails (#82)

* feat: display detailed error messages when prepare step fails

- Capture prepare step errors in action.yml (up to 2000 chars)
- Add error details to comment update with collapsible section
- Handle both prepare and Claude execution failures separately
- Add test coverage for error detail display

This helps users debug issues like git errors, permission problems,
and branch creation failures more easily.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

* refactor: simplify error capture to show clean error messages only

- Remove complex shell script that captured full output logs
- Use core.setOutput in prepare.ts to pass clean error message directly
- Avoid exposing potentially sensitive information from logs
- Show only the actual error message (e.g. 'Failed to fetch issue data')

This provides cleaner, more readable error messages without the risk
of exposing sensitive information from debug logs.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

* refactor: simplify error display to show clean error messages only

- Remove collapsible <details> section for error messages
- Display errors in simple code blocks since messages are now clean and short
- Makes error messages more direct and readable

🤖 Generated with [Claude Code](https://claude.ai/code)

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

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/github/operations/comment-logic.ts

@@ -15,6 +15,7 @@ export type CommentUpdateInput = {
   prLink?: string;
   branchName?: string;
   triggerUsername?: string;
+  errorDetails?: string;
 };
 
 export function ensureProperlyEncodedUrl(url: string): string | null {
@@ -75,6 +76,7 @@ export function updateCommentBody(input: CommentUpdateInput): string {
     actionFailed,
     branchName,
     triggerUsername,
+    errorDetails,
   } = input;
 
   // Extract content from the original comment body
@@ -177,7 +179,14 @@ export function updateCommentBody(input: CommentUpdateInput): string {
   }
 
   // Build the new body with blank line between header and separator
-  let newBody = `${header}${links}\n\n---\n`;
+  let newBody = `${header}${links}`;
+
+  // Add error details if available
+  if (actionFailed && errorDetails) {
+    newBody += `\n\n\`\`\`\n${errorDetails}\n\`\`\``;
+  }
+
+  newBody += `\n\n---\n`;
 
   // Clean up the body content
   // Remove any existing View job run, branch links from the bottom