Markdown Mint v0.8.0

• Add a Mermaid template picker with 13 examples across 10 diagram types,
  vertical/horizontal flowchart variants, and a live preview of the current
  code. Open the picker for a new insertion without selected Mermaid code, and
  open selected Mermaid code and existing diagrams directly in code editing.
• Confirm replacement of existing or edited code, restore the previous code
  with its caret and scroll position, and commit only through Insert/Update.
  Share the existing lazy local runtime, strict rendering, SVG sanitization,
  and source/history guards across document and modal previews.
• Preserve Git graph connector, commit, and label rendering under the strict
  content security policy.
• Keep Mermaid template navigation above the code editor heading and remove
  the modal-only replacement restore action. Replacement confirmation remains,
  and committed Markdown changes use normal document Undo/Redo.