fix: ensure Windows finds sidecar DLLs by setting PATH and CWD

The sidecar was crashing (exitCode: null) when invoked from Tauri
because Windows couldn't locate onnxruntime.dll in the sidecar directory.

Added setup_cmd() helper that:
- Adds the sidecar directory to the child process PATH
- Sets the child process CWD to the sidecar directory

This ensures Windows can find all required DLLs when Tauri invokes
the sidecar, matching the behavior of manual command-line execution.

src-tauri/src/transcription/sherpa_onnx.rs

@@ -132,8 +132,19 @@ impl Transcriber for SherpaOnnxTranscriber {
 ///    `CARGO_MANIFEST_DIR` (produção empacotado e dev)
 /// 3. nome nu `sherpa-onnx-offline` (PATH do sistema, dev, CI)
 fn locate_sidecar(sidecar_name: &str, manifest_dir: &str) -> Command {
+    fn setup_cmd(cmd: &mut Command, exe_path: &std::path::Path) {
+        if let Some(exe_dir) = exe_path.parent() {
+            if let Ok(current_path) = std::env::var("PATH") {
+                cmd.env("PATH", format!("{};{}", exe_dir.display(), current_path));
+            }
+            cmd.current_dir(exe_dir);
+        }
+    }
+
     if let Ok(path) = std::env::var("SHERPA_ONNX_SIDECAR") {
-        return Command::new(path);
+        let mut cmd = Command::new(&path);
+        setup_cmd(&mut cmd, std::path::Path::new(&path));
+        return cmd;
     }
     let manifest_path = std::path::Path::new(manifest_dir);
     if let Some(parent) = manifest_path.parent() {
@@ -143,7 +154,9 @@ fn locate_sidecar(sidecar_name: &str, manifest_dir: &str) -> Command {
         ];
         for candidate in candidates {
             if candidate.exists() {
-                return Command::new(candidate);
+                let mut cmd = Command::new(&candidate);
+                setup_cmd(&mut cmd, &candidate);
+                return cmd;
             }
         }
     }
@@ -155,7 +168,9 @@ fn locate_sidecar(sidecar_name: &str, manifest_dir: &str) -> Command {
     ];
     for candidate in manifest_candidates {
         if candidate.exists() {
-            return Command::new(candidate);
+            let mut cmd = Command::new(&candidate);
+            setup_cmd(&mut cmd, &candidate);
+            return cmd;
         }
     }
     Command::new(sidecar_name)