`spawn start ENOENT` error on Windows when adding account

[Foadsf]

Description:
When attempting to add an account using gmcli accounts add <email> on Windows, the process crashes with a spawn start ENOENT error. This prevents the automatic browser authorization flow from working.

The issue appears to be that the code attempts to spawn start directly. On Windows, start is a shell built-in command (part of cmd.exe), not a standalone executable, so spawn cannot find it unless run within a shell context.

Steps to Reproduce:

1. On a Windows machine (Node v22.14.0).
2. Run gmcli accounts add your.email@gmail.com.
3. The process crashes immediately with the error below.

Actual Behavior:

Error: spawn start ENOENT
    at ChildProcess._handle.onexit (node:internal/child_process:285:19)
    at onErrorNT (node:internal/child_process:483:16)
    at process.processTicksAndRejections (node:internal/process/task_queues:90:21)
Emitted 'error' event on ChildProcess instance at:
    at ChildProcess._handle.onexit (node:internal/child_process:291:12)
    ...
    errno: -4058,
    code: 'ENOENT',
    syscall: 'spawn start',
    path: 'start',

Environment:

• OS: Windows
• Node Version: v22.14.0
• gmcli Version: 0.1.0

Root Cause:
In src/gmail-oauth-flow.ts, the openBrowser method handles Windows by setting the command to start:

// src/gmail-oauth-flow.ts
private openBrowser(url: string): void {
    const cmd = process.platform === "darwin" ? "open" : process.platform === "win32" ? "start" : "xdg-open";
    spawn(cmd, [url], { detached: true, stdio: "ignore" });
}

Since spawn is called without { shell: true }, Node.js looks for an executable named start.exe or start.cmd, which does not exist.

Suggested Fix:
For Windows, the command should likely be executed via cmd.exe or by enabling the shell option.

Option A (Quick fix):
Change the spawn options to include shell: true (though this has security implications if input isn't sanitized, though here it's just the auth URL).

Option B (Safer Windows specific):

if (process.platform === "win32") {
    spawn("cmd.exe", ["/c", "start", "", url], { detached: true, stdio: "ignore" });
} else {
    // ... existing logic for mac/linux
}

Workaround:
Using the --manual flag works successfully as it bypasses the browser opening logic.