fix(workflows): change issue number types to string

GitHub Actions job outputs are always strings, so workflow_call inputs should be strings to avoid type coercion issues.

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

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

Author: MarkusNeusinger

.github/workflows/gen-library-impl.yml

@@ -16,11 +16,11 @@ on:
       main_issue_number:
         description: "Parent issue number"
         required: true
-        type: number
+        type: string
       sub_issue_number:
         description: "Sub-issue number for this library"
         required: true
-        type: number
+        type: string
       attempt:
         description: "Attempt number (1-3)"
         required: false