Initial release

• Document-based app for `.mmd` / `.mermaid` files plus pasted source, with a menu bar item that keeps it running after windows close.
• Diagram rendering with vendored mermaid.js 11.15.0 in a `WKWebView`, fully offline, with a custom light/dark theme that follows your preference.
• Preview/split toggle: look at the diagram, or edit the source alongside a live render (150 ms debounce).
• Zoom and fit: fills the window by default, manual zoom to 800% via slider and 50/100/200/400/800% presets, Shift + scroll to zoom, and Space + drag to pan. Crisp vector SVG.
• Local MCP server: agents connect via the bundled `neptunus-mcp` helper over a `0600` unix socket and call `preview_mermaid` to render a diagram here. `wait_for_review` blocks until you accept or reject and returns the verdict.
• Settings → MCP: live server status, a Restart control, connected clients, the helper path, and copy-paste `claude mcp add` / `.mcp.json` snippets. The menu bar mirrors the status.
• Export the diagram to SVG, PNG, or PDF.
• Dock icon only while a window is open; otherwise menu-bar-only, still running.
• Automatic updates via Sparkle.