Replace deprecated RESOURCE_URI_META_KEY with _meta.ui.resourceUri

Update all example servers to use the new recommended metadata format
for associating UI resources with tools. The old `RESOURCE_URI_META_KEY`
constant is deprecated in favor of the nested `_meta.ui.resourceUri`
structure.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

examples/cohort-heatmap-server/server.ts

@@ -6,7 +6,6 @@ import path from "node:path";
 import { z } from "zod";
 import {
   RESOURCE_MIME_TYPE,
-  RESOURCE_URI_META_KEY,
   registerAppResource,
   registerAppTool,
 } from "@modelcontextprotocol/ext-apps/server";
@@ -181,7 +180,7 @@ export function createServer(): McpServer {
         "Returns cohort retention heatmap data showing customer retention over time by signup month",
       inputSchema: GetCohortDataInputSchema.shape,
       outputSchema: CohortDataSchema.shape,
-      _meta: { [RESOURCE_URI_META_KEY]: resourceUri },
+      _meta: { ui: { resourceUri } },
     },
     async ({ metric, periodType, cohortCount, maxPeriods }) => {
       const data = generateCohortData(