fix: keep rendered images visible

[Azganoth]

Summary

• Render image NodeViews in normal block layout so decoded SVGs keep a visible box.
• Keep tiny and transparent images selectable on a paragraph-height editor surface while preserving their authored pixels.
• Cover renderable, linked, missing, and transparent image dimensions in the desktop suite.

Related Issue

Closes #490

Verification

• pnpm check:frontend — formatting, TypeScript, Oxlint, production build, and frontend coverage.
• pnpm test:e2e:desktop — rendered image geometry and the full assembled desktop suite.

Notes

• Rendered image borders were removed; error placeholders retain their dashed border as a resolution-state indicator.