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_api/src/supermaven_api.rs

@@ -212,7 +212,11 @@ pub async fn latest_release(
 }
 
 pub fn version_path(version: u64) -> PathBuf {
-    supermaven_dir().join(format!("sm-agent-{}", version))
+    supermaven_dir().join(format!(
+        "sm-agent-{}{}",
+        version,
+        std::env::consts::EXE_SUFFIX
+    ))
 }
 
 pub async fn has_version(version_path: &Path) -> bool {