Windows platform support and multi-instance workspace fix

[intisy]

Adds full Windows support and fixes workspace resolution when running multiple OpenCode instances.

[Nomadcxx]

Thanks man, this looks interesting, let me investigate.

[Nomadcxx]

Hey @intisy, thanks for the PR mate — Windows support is definitely needed and your contribution sparked this work.

I've opened a reworked version in #55 that builds on your idea but fixes a few issues I found during review:

• Kept as ESM () — changing it to commonjs would've broken all existing consumers
• Kept intact — gutting it to return true always would've caused proxy hijacking between different workspaces. The actual Windows multi-instance bug was a one-liner in canonicalizePathForCompare (not lowercasing on win32)
• Replaced the execSync(binary + " models") string concat with execFileSync to remove the command injection vector
• Rewrote the Node fallback grep/glob with correct regex escaping, proper newline splitting, and discriminated catch blocks
• Removed the chat.headers hook since it doesn't exist in the OpenCode plugin SDK

You're credited as co-author on all the commits. Appreciate the contribution — the binary resolution approach and provider detection were solid.