fix(cli): handle permission errors when configuring shell PATH (#1040)

## Summary

resolve #1034 

- Add write permission check in `install.sh` `add_bin_to_path`: exits
immediately with a clear error message when shell config files
(`.zshenv`, `.zshrc`, etc.) are not writable, instead of silently
failing and showing misleading success output
- Add `try/catch` around `SetEnvironmentVariable` in `install.ps1`
`Configure-UserPath`: exits with an actionable error message when PATH
update fails

---------

Co-authored-by: MK (fengmk2) <fengmk2@gmail.com>

Author: kazupon

packages/cli/install.ps1

@@ -178,9 +178,13 @@ function Configure-UserPath {
     }
 
     $newPath = "$binPath;$userPath"
-    [Environment]::SetEnvironmentVariable("Path", $newPath, "User")
-    $env:Path = "$binPath;$env:Path"
-    return "true"
+    try {
+        [Environment]::SetEnvironmentVariable("Path", $newPath, "User")
+        $env:Path = "$binPath;$env:Path"
+        return "true"
+    } catch {
+        Write-Error-Exit "Cannot update user PATH. Please check your system permissions and re-run the installer."
+    }
 }
 
 # Run vp env setup --refresh, showing output only on failure

packages/cli/install.sh

@@ -325,6 +325,10 @@ add_bin_to_path() {
   ref_pattern=$(printf '%s' "$INSTALL_DIR_REF" | sed 's/[.[\*^$()+?{|]/\\&/g')
 
   if [ -f "$shell_config" ]; then
+    if [ ! -w "$shell_config" ]; then
+      warn "Cannot write to $shell_config (permission denied), skipping."
+      return 1
+    fi
     if grep -q "${abs_pattern}/env" "$shell_config" 2>/dev/null || \
        grep -q "${ref_pattern}/env" "$shell_config" 2>/dev/null; then
       return 2