[ai-assisted] fix(mcp): coerce string params to numbers in set_fill_color, set_stroke_color, set_corner_radius

MCP clients may pass numeric parameters as strings. Add Number() coercion
in the WebSocket client transform layer so Figma plugin validation doesn't
reject them with "Expected number, received string".

Also adds a missing transform handler for set_corner_radius.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: JooHyung Park

src/main/server/shared/websocket-client.ts

@@ -203,23 +203,28 @@ export class WebSocketClient {
       transformedParams = {
         nodeId: params.nodeId,
         color: {
-          r: params.r,
-          g: params.g,
-          b: params.b,
-          a: params.a ?? 1,
+          r: Number(params.r),
+          g: Number(params.g),
+          b: Number(params.b),
+          a: Number(params.a ?? 1),
         },
       };
     } else if (command === 'set_stroke_color' && 'r' in params && 'g' in params && 'b' in params) {
       // Transform: { nodeId, r, g, b, a, weight } → { nodeId, color: { r, g, b, a }, weight }
       transformedParams = {
         nodeId: params.nodeId,
         color: {
-          r: params.r,
-          g: params.g,
-          b: params.b,
-          a: params.a ?? 1,
+          r: Number(params.r),
+          g: Number(params.g),
+          b: Number(params.b),
+          a: Number(params.a ?? 1),
         },
-        weight: params.weight ?? 1,
+        weight: Number(params.weight ?? 1),
+      };
+    } else if (command === 'set_corner_radius' && 'radius' in params) {
+      transformedParams = {
+        ...params,
+        radius: Number(params.radius),
       };
     }