Remove DNS lookup fallback from PowerShell OSC 7

Co-authored-by: sawka <2722291+sawka@users.noreply.github.com>

Author: Copilot

pkg/util/shellutil/shellintegration/pwsh_wavepwsh.sh

@@ -21,14 +21,11 @@ function Global:_waveterm_si_blocked {
 function Global:_waveterm_si_osc7 {
     if (_waveterm_si_blocked) { return }
 
-    # Get hostname with fallback chain
+    # Get hostname (allow empty for file:/// format)
     $hostname = $env:COMPUTERNAME
     if (-not $hostname) {
         $hostname = $env:HOSTNAME
     }
-    if (-not $hostname) {
-        $hostname = [System.Net.Dns]::GetHostName()
-    }
 
     # Percent-encode the raw path as-is (handles UNC, drive letters, etc.)
     $encoded_pwd = [System.Uri]::EscapeDataString($PWD.Path)