feat: Add design guidelines and improve basic view structure

[dominikriemer]

Purpose

• Add product and design guidelines for consistent UI development.
• Modernize the iconbar, toolbar, breadcrumbs, basic views, navigation tabs, and reusable page header.
• Apply the unified page structure across pipelines, adapters, datasets, dashboards, charts, assets, profile, help, and the pipeline editor.
• Harmonize the Extensions Installation layout with responsive controls and grids.
• Redesign asset view and edit pages, including responsive asset navigation, clearer metadata, and consolidated tree actions.

Remarks

PR introduces (a) breaking change(s): no

PR introduces (a) deprecation(s): no