fix: set UTF-8 input encoding for Windows stdin reading

On Windows systems with a non-UTF-8 system codepage, [Console]::In.ReadToEnd()
decodes UTF-8 stdin using the system codepage instead of UTF-8. This corrupts
non-ASCII characters and breaks JSON parsing for hooks that receive non-ASCII
data (e.g. PreToolUse with AskUserQuestion containing non-English text).

Fix: set [Console]::InputEncoding to UTF-8 before reading stdin.

Author: alexyan0431

scripts/install-windows.ps1

@@ -1654,6 +1654,7 @@ $LogFile = "$ClaudeHome\logs\notifications.log"
 $HookData = ""
 try {
     if ([Console]::IsInputRedirected) {
+        [Console]::InputEncoding = [System.Text.Encoding]::UTF8
         $HookData = [Console]::In.ReadToEnd()
     }
 } catch {