[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-tools_list.json

@@ -0,0 +1,28 @@
+{
+  "tools": [
+    {
+      "name": "get_weather",
+      "description": "Get current weather for a city",
+      "inputSchema": {
+        "type": "object",
+        "properties": {
+          "city": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "city"
+        ]
+      },
+      "_meta": {
+        "ui": {
+          "resourceUri": "ui://weather-app",
+          "visibility": [
+            "model",
+            "app"
+          ]
+        }
+      }
+    }
+  ]
+}