fix: high-quality sampling for downscaled app icons

[xav-ie]

Problem

App icons in the bar (icon.background.image=app.<bundle-id>) render with
visible jagged/aliased edges instead of a clean downscaled icon.

The bar's window context is created with kCGInterpolationNone (window.c),
which is the right default for the bar's pixel-exact PNG/alias icons — they are
drawn 1:1 and stay crisp. App icons are the exception: workspace_icon_for_app
returns the app's NSImage at its native representation size (often 128px+),
which then gets scaled down to the item's icon size at draw time. Downscaling
with nearest-neighbour sampling decimates the image, producing the aliasing.

Fix

In image_draw, sample only the sources that are genuinely rescaled — app
icons, space previews, and linked media artwork — with kCGInterpolationHigh
for the CGContextDrawImage call, then restore kCGInterpolationNone.

File-backed image icons and text are unaffected: they draw 1:1 or ignore
interpolation quality entirely, so they stay pixel-crisp as before.

Notes

• Scoped by checking image->path for the app./space. prefixes (plus the
  image->link media-artwork case), so the crisp default is preserved for
  everything else.
• No API/config surface change; purely a rendering-quality fix.

Testing

Before/after screenshots of a front_app-style item showing the app icon:

before	after_