fix(sdk): add shell option for Windows spawn compatibility

[jc01rho]

Summary

• Adds shell: process.platform === 'win32' to both spawn() calls in SDK server module
• Fixes Windows compatibility issue where npm-installed .cmd wrappers aren't found

Fixes #8160

Problem

On Windows, npm-installed packages create .cmd wrapper scripts (e.g., opencode.cmd). Node.js spawn() without shell: true cannot find these in PATH, causing:

ENOENT: no such file or directory, uv_spawn 'opencode'

Solution

Add conditional shell: true on Windows:

const proc = spawn(\, args, {
  signal: options.signal,
  shell: process.platform === 'win32',  // NEW
  env: { ... },
})

Testing

Verified manually on Windows 11:

1. Before fix: ENOENT error when calling createOpencodeServer()
2. After fix: Server spawns successfully, returns URL

Files Changed

• packages/sdk/js/src/server.ts - both spawn calls
• packages/sdk/js/src/v2/server.ts - both spawn calls

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found:

• PR fix: resolve Windows spawn ENOENT error in SDK #2813: "fix: resolve Windows spawn ENOENT error in SDK"
  fix: resolve Windows spawn ENOENT error in SDK #2813

Reason for related flag: This PR appears to address the same Windows spawn ENOENT error issue that PR #8162 is fixing. Both target SDK compatibility with Windows .cmd wrapper scripts and the spawn() function error. You may want to verify if #2813 is already merged/closed or if it's a different approach to the same problem.