refactor(framemode): unify connected surface chrome via SDF pipeline

- Shadow system rewrite with SDF quads
- Replace ConnectedShape/layer FBOs w/frame & chrome SDF shaders
- Improve frame blur performance
- Plugin performance gate

quickshell/Common/Theme.qml

@@ -911,6 +911,16 @@ Singleton {
         }
         return Qt.rgba(r, g, b, alpha);
     }
+    function elevationAmbient(level) {
+        const blur = (level && level.blurPx !== undefined) ? Math.max(0, level.blurPx) : 0;
+        const alpha = ((level && level.alpha !== undefined) ? level.alpha : 0.3) * 0.5;
+        return {
+            blurPx: blur * 1.75,
+            spreadPx: 1,
+            alpha: alpha
+        };
+    }
+
     function elevationTintOpacity(level) {
         if (!level)
             return 0;