Copy only the assessed provider's PNG icons into reports

[bencehezso]

Summary

Every report bundled the full icon tree — 2,204 files, 5.5 MB — to display a handful of icons. copy_assets() now copies only the assessed provider's icon folder, and only PNGs.

Report	Before	After
AWS	6.58 MB	1.89 MB	−71%
Azure	6.50 MB	2.88 MB	−56%

What changes

• copy_assets() takes cloud_service_provider and copies icons/<provider>/ plus icons/severity/ and icons/misc/. The severity icons are used by the PDF renderer and no_image.png is the fallback, so both travel with every report. cloud_service_provider was already a parameter at the call site — nothing new to plumb through.

• PNG only. No renderer loads an icon SVG; they were dead weight. The ignore callable is an allowlist (keep directories, keep .png, drop the rest) rather than ignore_patterns("*.svg"), so a future stray file type can't ride along. Category subfolders are preserved.