diag(packaging/windows): isolate the ISCC "path not found" failure

All [Files] sources are validated-present yet ISCC still errors before any
"Compiling" output (no line number) — so it's startup/[Setup]-internal, not a
source path. Add an explicit [Languages] (compiler:Default.isl) to rule out the
auto-added default language, and on ISCC failure dump the Inno install dir +
run a trivial [Setup]-only smoke script to tell "Inno broken" from "my script".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packaging/windows/punktfunk-host.iss

@@ -55,6 +55,9 @@ WizardStyle=modern
 UninstallDisplayName=punktfunk host {#MyAppVersion}
 UninstallDisplayIcon={app}\punktfunk-host.exe
 
+[Languages]
+Name: "english"; MessagesFile: "compiler:Default.isl"
+
 [Tasks]
 #ifdef WithDriver
 Name: "installdriver"; Description: "Install the SudoVDA virtual display driver (required for native-resolution streaming)"