fix: replace broken LaMa watermark detection with median filter approach

The luminance anomaly detection + LaMa inpainting approach failed because
watermark signal on the matted foreground was too weak (10-15 units vs
threshold of 25). Median filter with kernel=5 effectively removes
semi-transparent watermark text while preserving the stamp structure.

Pipeline is now: median filter (if toggle on) -> BiRefNet matting -> defringe.
No longer requires object-eraser-colorize bundle for watermark removal.

apps/web/src/components/tools/transparency-fixer-settings.tsx

@@ -2,7 +2,6 @@ import { ChevronDown, ChevronRight, Droplets } from "lucide-react";
 import { useEffect, useRef, useState } from "react";
 import { ProgressCard } from "@/components/common/progress-card";
 import { useToolProcessor } from "@/hooks/use-tool-processor";
-import { useFeaturesStore } from "@/stores/features-store";
 import { useFileStore } from "@/stores/file-store";
 
 type OutputFormat = "png" | "webp";
@@ -23,14 +22,6 @@ export function TransparencyFixerControls({
   const [removeWatermark, setRemoveWatermark] = useState(false);
   const [advancedOpen, setAdvancedOpen] = useState(false);
 
-  const eraserInstalled = useFeaturesStore((s) => s.isToolInstalled("erase-object"));
-  const featuresLoaded = useFeaturesStore((s) => s.loaded);
-  const fetchFeatures = useFeaturesStore((s) => s.fetch);
-
-  useEffect(() => {
-    fetchFeatures();
-  }, [fetchFeatures]);
-
   const onChangeRef = useRef(onChange);
   useEffect(() => {
     onChangeRef.current = onChange;
@@ -40,8 +31,6 @@ export function TransparencyFixerControls({
     onChangeRef.current({ defringe, outputFormat, removeWatermark });
   }, [defringe, outputFormat, removeWatermark]);
 
-  const toggleDisabled = featuresLoaded && !eraserInstalled;
-
   return (
     <div className="space-y-3">
       <p className="text-xs text-muted-foreground">
@@ -55,9 +44,7 @@ export function TransparencyFixerControls({
           <div>
             <p className="text-xs font-medium">Remove Watermark</p>
             <p className="text-[10px] text-muted-foreground">
-              {toggleDisabled
-                ? "Requires Object Eraser bundle"
-                : "Detect and remove semi-transparent watermarks"}
+              Detect and remove semi-transparent watermarks
             </p>
           </div>
         </div>
@@ -65,11 +52,10 @@ export function TransparencyFixerControls({
           type="button"
           data-testid="remove-watermark-toggle"
           aria-pressed={removeWatermark}
-          disabled={toggleDisabled}
           onClick={() => setRemoveWatermark(!removeWatermark)}
           className={`relative inline-flex h-5 w-9 items-center rounded-full transition-colors ${
             removeWatermark ? "bg-primary" : "bg-muted"
-          } ${toggleDisabled ? "opacity-50 cursor-not-allowed" : ""}`}
+          }`}
         >
           <span
             className={`inline-block h-3.5 w-3.5 rounded-full bg-white transition-transform ${