Zoom + minimap + auto-layout inside the ER diagram webview

[FROWNINGdev]

Mermaid alone does not ship pan/zoom or a minimap. On a schema with 50+ models, the diagram becomes hard to navigate.

Ask:

• Wrap the rendered SVG with svg-pan-zoom or an equivalent (needs to be inlined for the CSP nonce)
• Add a minimap overlay in a webview corner
• Add an "Auto-layout" button that reflows the SVG

Constraints:

• Must respect the current CSP: no CDN scripts except https://cdn.jsdelivr.net for Mermaid itself, script nonces required.
• Must survive theme changes without a full webview reload.

Where to look: src/graphWebview.ts.

Medium complexity. A great contribution for someone comfortable with SVG + webview messaging.