fix: handle Windows path stripping failures gracefully (#93)

## Summary
- Fix Windows path handling that caused "Invalid relative path" errors
- On Windows, path stripping may fail due to case sensitivity or path format differences
- Instead of failing with an error, treat such paths as outside the workspace (like other unmatched paths)

## Problem
When running vite-task on Windows, paths tracked by fspy might have different formats or casing than the workspace root. This caused errors like:
```
Invalid relative path 'D:\a\vite-plus\vite-plus\ecosystem-ci\tanstack-start-helloworld': path is not relative
```

## Solution
Changed the error handling to use `.ok()` instead of `.map_err()` followed by `.transpose()?`, treating conversion failures as paths outside the workspace.

## Test plan
- [x] Ran `cargo test -p vite_task` locally
- Testing in vite-plus E2E CI

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: branchseer

crates/vite_task/src/session/execute/spawn.rs

@@ -174,17 +174,15 @@ where
     let path_writes = &mut track_result.path_writes;
 
     for access in termination.path_accesses.iter() {
-        let relative_path = access
-            .path
-            .strip_path_prefix(workspace_root, |strip_result| {
-                let Ok(stripped_path) = strip_result else {
-                    return None;
-                };
-                Some(RelativePathBuf::new(stripped_path).map_err(|err| {
-                    anyhow::anyhow!("Invalid relative path '{}': {}", stripped_path.display(), err)
-                }))
-            })
-            .transpose()?;
+        let relative_path = access.path.strip_path_prefix(workspace_root, |strip_result| {
+            let Ok(stripped_path) = strip_result else {
+                return None;
+            };
+            // On Windows, paths are possible to be still absolute after stripping the workspace root.
+            // For example: c:\workspace\subdir\c:\workspace\subdir
+            // Just ignore those accesses.
+            RelativePathBuf::new(stripped_path).ok()
+        });
 
         let Some(relative_path) = relative_path else {
             // Ignore accesses outside the workspace