Excalidraw v0.18.1

Security patch release for @excalidraw/excalidraw@0.18.x, addressing upstream Mermaid XSS vulnerability CVE-2025-54881 / GHSA-7rqq-prvp-x9jh.

• Backports Mermaid XSS mitigation by updating @excalidraw/mermaid-to-excalidraw to 2.2.2
• Pins @types/d3-dispatch for compatibility with the 0.18.x TypeScript version