Oversample small SVG icons before rasterization

[anthony-firn]

Oversample small SVG icons before rasterization

Summary

Small SVG icons are currently rasterized at their final draw size. That leaves very little coverage information for curved edges and diagonal strokes, which shows up as rough launcher and greeter icons at common 16-32 px sizes.

This change rasterizes small SVGs at 2x size in the shared wgpu and tiny_skia vector backends, then lets the existing image draw path scale them back down into the requested bounds.

Why this shape

• It keeps the change in the shared renderer path instead of adding app-specific workarounds.
• It only oversamples small icons, so the extra cache and raster cost stays bounded.
• It applies to both renderer backends used by COSMIC surfaces.

Validation

• Built cosmic-launcher against the patched renderer path.
• Verified the centered launcher still rendered its result text correctly.
• Compared launcher app-icon crops against the stock renderer output and confirmed visibly smoother small icons with no meaningful text regression.

[anthony-firn]

Closing this for now to keep review focused on #318, which is the active renderer-side fix for the dock issue. This can be reopened later if a separate SVG follow-up still makes sense.