Asset browser with preview API

Current State

The Asset Browser shows a list of assets by name/icon but has no visual preview of asset contents (texture thumbnails, model wireframes, material swatches, audio waveforms, etc.).

Tasks:

• Design the asset preview provider API (same as Inspector preview, shared system)
• Implement thumbnail generation pipeline (render-to-texture for 3D assets)
• Implement texture asset preview (small thumbnail of the image)
• Implement model/mesh preview (wireframe or rendered thumbnail)
• Implement material preview (sphere/quad with material applied)
• Implement audio preview (waveform visualization)
• Implement preview caching (disk cache for generated thumbnails)
• Implement virtualized grid/list layout with preview thumbnails
• Support multiple preview sizes (small, medium, large icons)
• Show preview in a dedicated preview panel when selecting an asset

Acceptance Criteria:

• Asset Browser shows visual thumbnails for all supported asset types
• Texture assets display a miniature version of the image
• Model assets display a wireframe or shaded thumbnail
• Material assets display a swatch with the material applied to a sphere
• Audio assets display a waveform preview
• Thumbnails are cached on disk and regenerated only when the source changes
• Preview size can be adjusted (small/medium/large)
• Selecting an asset shows a larger preview in a dedicated panel

Related: