Feature highlight: Move issues between projects

What this post added

Introduced the ability to move issues between projects. This involved copying the original issue, closing it, and referencing it in the new location. A significant technical challenge was updating cross-project references (e.g., `#123`, `!456`) within issue descriptions and comments to correctly point to the original project. This was solved by implementing a mechanism that matches local references, substitutes them with cross-project references, and validates the substitution by comparing generated HTML. This also necessitated improvements to Markdown cross-project reference notation for labels.