feat(SaveImageLM): expose webp_method and jpeg_subsampling as conditional node inputs

Add two new optional parameters to the Save Image node:

- webp_method (INT, 0-6, default 6): Controls WebP compression level.
  0=fastest/largest, 6=slowest/smallest. Previously hardcoded to 0.
- jpeg_subsampling (INT, 0-2, default 0): Controls JPEG chroma
  subsampling. 0=4:4:4 (best quality), 1=4:2:2, 2=4:2:0.

Frontend JS extension hides/disables each parameter when the
selected file_format doesn't apply (e.g., webp_method is hidden
when saving as PNG or JPEG). 7 new tests cover parameter plumbing
and default consistency across INPUT_TYPES, save_images(), and
process_image().

web/comfyui/save_image_extra_output.js

@@ -130,6 +130,35 @@ app.registerExtension({
       widget.serializeValue = () => {
         return applyTextReplacements(widget.value);
       };
+
+      // --- Conditional widget visibility for webp_method / jpeg_subsampling ---
+      const formatWidget = getWidgetByName(this, "file_format");
+      const webpMethodWidget = getWidgetByName(this, "webp_method");
+      const jpegSubWidget = getWidgetByName(this, "jpeg_subsampling");
+
+      function updateFormatConditional() {
+        const fmt = formatWidget?.value;
+        if (webpMethodWidget) {
+          webpMethodWidget.disabled = fmt !== "webp";
+          webpMethodWidget.hidden = fmt !== "webp";
+        }
+        if (jpegSubWidget) {
+          jpegSubWidget.disabled = fmt !== "jpeg";
+          jpegSubWidget.hidden = fmt !== "jpeg";
+        }
+      }
+
+      // Set initial state
+      updateFormatConditional();
+
+      // Watch for format changes
+      if (formatWidget) {
+        const origCallback = formatWidget.callback;
+        formatWidget.callback = function (value) {
+          origCallback?.call(this, value);
+          updateFormatConditional();
+        };
+      }
     });
   },
 });