fix(env): unset session override when vp env use called without arguments

Fixes #951

When `vp env use` is called without a version argument, it should revert
to file-based Node.js version resolution instead of keeping the session
override from `VITE_PLUS_NODE_VERSION` env var or session file.

Changes:
- Add `resolve_version_from_files()` to resolve version skipping session overrides
- Update `vp env use` to unset session override before resolving when no arg provided
- This allows users to temporarily override with `vp env use 22` and revert with `vp env use`

Author: JasonOA888

crates/vite_global_cli/src/commands/env/config.rs

@@ -230,6 +230,13 @@ pub async fn resolve_version(cwd: &AbsolutePath) -> Result<VersionResolution, Er
         });
     }
 
+    resolve_version_from_files(cwd).await
+}
+
+/// Resolve Node.js version from project files only (skipping session overrides).
+///
+/// This is used by `vp env use` without arguments to revert to file-based resolution.
+pub async fn resolve_version_from_files(cwd: &AbsolutePath) -> Result<VersionResolution, Error> {
     let provider = NodeProvider::new();
 
     // Use shared version resolution with directory walking

crates/vite_global_cli/src/commands/env/use.rs

@@ -94,11 +94,19 @@ pub async fn execute(
     let provider = vite_js_runtime::NodeProvider::new();
 
     // Resolve version: explicit argument or from project files
+    // When no argument provided, unset session override and resolve from project files
     let (resolved_version, source_desc) = if let Some(ref ver) = version {
         let resolved = config::resolve_version_alias(ver, &provider).await?;
         (resolved, format!("{ver}"))
     } else {
-        let resolution = config::resolve_version(&cwd).await?;
+        // No version argument - unset session override first
+        if has_eval_wrapper() {
+            println!("{}", format_unset(&shell));
+        } else {
+            config::delete_session_version().await?;
+        }
+        // Now resolve from project files (not from session override)
+        let resolution = config::resolve_version_from_files(&cwd).await?;
         let source = resolution.source.clone();
         (resolution.version, source)
     };