Tune drag capture frame shadows

[yvette-carlisle]

Summary

• split capture-frame shadows by source kind
• keep window captures on the existing cinematic profile
• use a lighter document-style shadow profile for dragged regions and add a render regression test for top-shadow darkness

Verification

• cargo test -p rsnap-capture-core capture_frame
• cargo make fmt-rust-check
• cargo make check-rust
• cargo make check-vstyle-rust
• ./scripts/build_and_run.sh --verify