fix: resolve MarkiTect issue handling system integration problems (issue #120)

- Fix issue manager to properly read API token and repo info from main MarkiTect config
- Update Gitea plugin to use correct repository-specific API endpoints
- Correct domain model mapping to only include valid Issue model fields
- Fix presentation layer to safely access optional body attribute
- Enable full functionality for 'markitect issues show' and 'markitect issues list' commands

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

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

cli/presenters/views.py

@@ -120,7 +120,8 @@ class IssueView:
             print(f"   Status: {issue.state.upper()} | Created: {issue.created_at.strftime('%Y-%m-%d')}")
 
             # Truncate body for list view
-            body_preview = issue.body[:80] + "..." if len(issue.body) > 80 else issue.body
+            body = getattr(issue, 'body', '')
+            body_preview = body[:80] + "..." if len(body) > 80 else body
             if body_preview:
                 print(f"   {body_preview}")
             OutputFormatter.empty_line()
@@ -143,7 +144,8 @@ class IssueView:
             print(f"   Created: {created} | Updated: {updated}")
 
             # Truncate body for list view
-            body_preview = issue.body[:80] + "..." if len(issue.body) > 80 else issue.body
+            body = getattr(issue, 'body', '')
+            body_preview = body[:80] + "..." if len(body) > 80 else body
             if body_preview:
                 print(f"   {body_preview}")
             OutputFormatter.empty_line()