Built-in configuration for auto-centering diagrams with palette space reservation

[gaosen1]

Is your feature request related to a problem? Please describe.

Yes, I'm always frustrated when I open a BPMN diagram and parts of the workflow are hidden behind the left-side palette/toolbar. The canvas.zoom('fit-viewport') centers the diagram within the entire container, but doesn't account for the palette space, forcing users to manually drag and zoom to see the complete diagram.
Current behavior:

• Diagram is centered in the full container (including palette area)
• Left-side palette overlaps with workflow content
• Users must manually adjust view to see hidden elements
• Poor initial user experience

Describe the solution you'd like

Built-in configuration option that automatically reserves space for the left-side palette when using fit-viewport:

const modeler = new BpmnModeler({
  container: containerRef.current,
  // New configuration
  autoFit: {
    enabled: true,
    paletteSpace: 'auto', // automatically detect palette width
    margin: 20 // additional buffer space
  }
});

Expected behavior:

• canvas.zoom('fit-viewport') automatically detects palette width
• Diagram is centered within the available space (container minus palette)
• No content overlap with the palette
• Immediate optimal view without manual adjustment

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.
Current workaround (implemented):

// 1. Temporarily adjust container width
container.style.width = `calc(100% - ${paletteWidth + 20}px)`;

// 2. Apply fit-viewport with adjusted container
canvas.zoom('fit-viewport');

// 3. Restore container and fine-tune position
container.style.width = originalWidth;
const viewbox = canvas.viewbox();
viewbox.x = viewbox.x - paletteWidth - 100;
canvas.viewbox(viewbox);

Additional context

Environment:

• BPMN.js version: 18.4.0
• Browser: macos chrome version 139.0.7258.128

My application is like this, and the left-side palette overlaps with workflow content: