feat(kyber-linux): auto-download KyberLauncher.exe if not present

Instead of erroring when the installer is missing, attempt to fetch it
automatically: first scrape kyber.gg for a direct .exe link, then fall
back to a known CDN path. If download fails, print the manual instruction
and exit cleanly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D8ckUJQtj1pH8jtAddBDZs

scripts/setup-kyber-linux.sh

@@ -85,15 +85,38 @@ STEAM_HOME=$(find_steam_home) || {
 }
 echo "Steam home: $STEAM_HOME"
 
-# ── Verify Kyber installer ─────────────────────────────────────────────────
+# ── Verify / download Kyber installer ─────────────────────────────────────
 if [ ! -f "$KYBER_INSTALLER" ]; then
     echo ""
-    echo "ERROR: Kyber installer not found at: $KYBER_INSTALLER"
+    echo "Kyber installer not found at: $KYBER_INSTALLER"
+    echo "Attempting to download KyberLauncher.exe from kyber.gg..."
+    mkdir -p "$(dirname "$KYBER_INSTALLER")"
+    # Try to find the download link on kyber.gg, then fall back to known URLs.
+    echo "  Checking kyber.gg for the download link..."
+    KYBER_DL_URL=""
+    # Extract the first .exe href from the kyber.gg download page
+    _raw=$(curl -sL --max-time 15 "https://kyber.gg/download" 2>/dev/null || \
+           curl -sL --max-time 15 "https://kyber.gg" 2>/dev/null)
+    if [ -n "$_raw" ]; then
+        KYBER_DL_URL=$(echo "$_raw" | grep -oP 'https?://[^"'\''<>\s]+KyberLauncher\.exe' | head -1)
+    fi
+    # Known fallback locations (update these if kyber.gg changes hosting)
+    if [ -z "$KYBER_DL_URL" ]; then
+        KYBER_DL_URL="https://cdn.kyber.gg/builds/KyberLauncher.exe"
+    fi
+    echo "  Downloading from: $KYBER_DL_URL"
+    if curl -L --progress-bar -o "$KYBER_INSTALLER" "$KYBER_DL_URL" \
+            && [ -s "$KYBER_INSTALLER" ]; then
+        echo "Downloaded: $KYBER_INSTALLER"
+    else
         echo ""
-    echo "Download KyberLauncher.exe from https://kyber.gg, then:"
+        echo "ERROR: Automatic download failed."
+        echo "Download KyberLauncher.exe manually from https://kyber.gg, then:"
         echo "  $0 /path/to/KyberLauncher.exe"
+        rm -f "$KYBER_INSTALLER"
         exit 1
     fi
+fi
 echo "Kyber installer: $KYBER_INSTALLER"
 
 # ── Locate Proton Experimental ─────────────────────────────────────────────