fix(windows): use platform_binary_name to resolve sparkle-mcp.exe path

[Gme-muriuki]

Problem

On Windows, after successfully installing a cargo crate, the binary existence check was looking for sparkle-mcp instead of sparkle-mcp.exe, causing the mod to fail to load with:
Binary sparkle-mcp not found after installing sparkle-mcp@0.5.1
This had a two-part effect:

1. cargo binstall would succeed and find no binary at the expected path, silently falling through to cargo install as if binstall had failed
2. cargo install would also succeed, but the same missing .exe check caused the final binary existence check to fail, surfacing the error to the user

This affected all cargo-distributed mods on Windows, including sparkle-mcp.

Fix

Added a platform_binary_name helper that appends .exe on Windows. Applied it to all three places where the binary path is constructed:

• install_cargo_crate_sync
• resolve_cargo
• resolve_distribution

Testing

Manually verified on Windows x86-64 -- sparkle-mcp now loads correctly in the Symposium VSCode extension.

[jackh726]

That'd probably do it. Guess we don't have a windows CI runner.