[Bug]: Unable to locate Codex CLI binaries. Ensure @openai/codex is installed with optional dependencies.

### Platform

Windows

### Operating system version

Windows 11

### System architecture

Intel (x86)

### PolyScope Version

latest

### Bug description

Codex on windows is unable to find binaries, and there is no option to set the path to use.

There is also no Polyscope option in the menubar.

### Steps to reproduce

1. Set agent to GPT
2. Type anything

### Relevant log output

```shell
[server:err] 'cp' is not recognized as an internal or external command,
[server:err] operable program or batch file.
[server:err] 'rm' is not recognized as an internal or external command,
[server:err] operable program or batch file.
[server:err] [checkpoint] failed to save: 143 | `;H.enqueue(L.encode(D))}async handleGetRequest(H){if(!H.headers.get("accept")?.includes("text/event-stream"))return this.createJsonErrorResponse(406,-32000,"Not Acceptable: Client must accept text/event-stream");let A=this.validateSession(H);if(A)return A;let $=this.validateProtocolVersion(H);if($)return $;if(this._eventStore){let U=H.headers.get("last-event-id");if(U)return this.replayEvents(U)}if(this._streamMapping.get(this._standaloneSseStreamId)!==void 0)return this.createJsonErrorResponse(409,-32000,"Conflict: Only one SSE stream is allowed per session");let I=new TextEncoder,D,M=new ReadableStream({start:(U)=>{D=U},cancel:()=>{this._streamMapping.delete(this._standaloneSseStreamId)}}),E={"Content-Type":"text/event-stream","Cache-Control":"no-cache, no-transform",Connection:"keep-alive"};if(this.sessionId!==void 0)E["mcp-session-id"]=this.sessionId;return this._streamMapping.set(this._standaloneSseStreamId,{controller:D,encoder:I,cleanup:()=>{this._streamMapping.delete(this._standaloneSseStreamId);try{

[server:err] 'cp' is not recognized as an internal or external command,
[server:err] operable program or batch file.
[server:err] signal: null,
[server:err] status: 1,
[server:err] output: [ null, "", "'cp' is not recognized as an internal or external command,\r\noperable program or batch file.\r\n" ],
[server:err] pid: 44632,
[server:err] stdout: "",
[server:err] stderr: "'cp' is not recognized as an internal or external command,\r\noperable program or batch file.\r\n",
[server:err] at genericNodeError (node:child_process:1010:22)
[server:err] at checkExecSyncError (node:child_process:470:27)
[server:err] at execSync (node:child_process:278:31)
[server:err] at N5H (B:/~BUN/root/polyscope-server-x86_64-pc-windows-msvc.exe:148:1606)
[server:err] at B:/~BUN/root/polyscope-server-x86_64-pc-windows-msvc.exe:220:5564
[server:err] at processTicksAndRejections (native:7:39)

[server] [agent] start error: Unable to locate Codex CLI binaries. Ensure @openai/codex is installed with optional dependencies.
```

Reproduce the GPT-agent flow on Windows 11 and start from the server's agent startup error and the logged cp/rm failures. Trace how the Codex CLI binaries are located and how checkpoint commands run; done means the agent starts without binary-location or shell-command errors and the Polyscope menu option is addressed.

Written by the indexing model from the issue text.