feat: Add Markdown issue template to support bug report pre-filling

GitHub's YAML templates (.yml) don't support URL parameter pre-filling, but
Markdown templates (.md) do. This adds a structured bug report template that
allows the automated bug reporter to pre-fill all user-submitted data.

Changes:
- Create .github/ISSUE_TEMPLATE/auto_bug_report.md template
- Update bug_report_api.py to use template=auto_bug_report.md parameter
- Update tests to verify template parameter is included in URL
- Add explanatory comments about YAML vs Markdown template differences

Benefits:
- Users see a structured bug report template (not generic issue form)
- All bug report data is pre-filled from the UI form
- Template provides consistent formatting and organization
- Better UX than generic issue creation

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

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

python/src/server/api_routes/bug_report_api.py

@@ -247,9 +247,10 @@ def _create_manual_submission_response(bug_report: BugReportRequest) -> BugRepor
 
     base_url = f"https://github.com/{github_service.repo}/issues/new"
 
-    # GitHub only supports title and body parameters for pre-filling
-    # Labels cannot be set via URL (requires API or manual selection)
+    # Use Markdown template for structured layout with URL pre-filling support
+    # YAML templates don't support URL parameters, but Markdown templates do
     params = {
+        "template": "auto_bug_report.md",
         "title": bug_report.title,
         "body": issue_body,
     }