[Examples][Tests] Make the MCP Apps example work over HTTP, and pin it (#439)

* [Examples][Tests] Make the MCP Apps example work over HTTP, and pin it

It was the only example without a session store, so every request under
`php -S` or php-fpm - each its own process - was answered "Session not found
or has expired". It now uses a FileSessionStore like the others.

Inspector snapshots pin what the extension actually puts on the wire: the
ui:// resource's `text/html;profile=mcp-app` MIME type and `ui` marker, and
the `_meta.ui` on the tool that links the two.

* Apply suggestion from @chr-hertel

* Apply suggestion from @chr-hertel

tests/Inspector/Http/snapshots/HttpMcpAppsTest-resources_list.json

@@ -0,0 +1,13 @@
+{
+  "resources": [
+    {
+      "name": "weather-app",
+      "uri": "ui://weather-app",
+      "description": "Interactive weather dashboard",
+      "mimeType": "text/html;profile=mcp-app",
+      "_meta": {
+        "ui": {}
+      }
+    }
+  ]
+}