[UI] Register page: Limit Page Width for Better Readability

### Severity

P3 - Medium (Minor functionality affected)

### MCP Server Creation Source

MCP Server in Api Center

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#### Description
Right now, the layout stretches to fill the entire width of the screen on large displays. While this works technically, it negatively affects readability.

#### Problem
When content spans the full width of wide screens, it becomes harder for users to scan and read. This can lead to visual fatigue or difficulty tracking lines of text.

#### Azure guidance
- https://eng.ms/docs/products/azure-portal-framework-ibizafx/designguide/templates/design-patterns-page-responsive-design

#### Current experience

#### Example of expectations
Centered

Left aligned

#### Azure Guidance