windows: Fix supermaven (#16203)

Closes #16194

This PR introduces the following changes:

1. Updated the download process to retrieve the `.exe` file, as the API
response indicates that the `.exe` file should be downloaded on Windows.
> API response:
"https://supermaven-public.s3.amazonaws.com/sm-agent/26/windows/amd64/sm-agent.exe"
2. Modified the startup behavior of supermaven to prevent the cmd window
from appearing.

Release Notes:

- N/A

crates/supermaven/Cargo.toml

@@ -31,6 +31,9 @@ text.workspace = true
 ui.workspace = true
 util.workspace = true
 
+[target.'cfg(target_os = "windows")'.dependencies]
+windows.workspace = true
+
 [dev-dependencies]
 editor = { workspace = true, features = ["test-support"] }
 env_logger.workspace = true

crates/supermaven/src/supermaven.rs

@@ -260,14 +260,21 @@ impl SupermavenAgent {
         client: Arc<Client>,
         cx: &mut ModelContext<Supermaven>,
     ) -> Result<Self> {
-        let mut process = Command::new(&binary_path)
+        let mut process = Command::new(&binary_path);
+        process
             .arg("stdio")
             .stdin(Stdio::piped())
             .stdout(Stdio::piped())
             .stderr(Stdio::piped())
-            .kill_on_drop(true)
-            .spawn()
-            .context("failed to start the binary")?;
+            .kill_on_drop(true);
+
+        #[cfg(target_os = "windows")]
+        {
+            use smol::process::windows::CommandExt;
+            process.creation_flags(windows::Win32::System::Threading::CREATE_NO_WINDOW.0);
+        }
+
+        let mut process = process.spawn().context("failed to start the binary")?;
 
         let stdin = process
             .stdin