fix(desktop): locate sensing server on Windows

[alloutflo]

Summary

• use sensing-server.exe and where on Windows while retaining the Unix names elsewhere
• select the first non-empty result when where returns multiple CRLF-separated matches
• cover both platform naming and multi-match parsing with regression tests

This repairs the sibling-binary and PATH lookup strategies without changing explicit custom paths.

Validation

• cargo test --manifest-path v2/Cargo.toml -p wifi-densepose-desktop commands::server::tests --no-default-features
• git diff --check upstream/main...HEAD

The Windows conventions are exercised platform-independently; no Windows runtime or packaging claim is made.

Closes #1517