[Server] Always emit items for array tool parameter schemas (#378)

Array tool parameters without an inferable element type generated `{"type":"array"}` with no `items`, which strict MCP clients (VS Code / Copilot) reject. Always emit `items` (`{}` when the element type is unknown) and recover the element type for nullable typed arrays such as `string[]|null`.

Fixes #151

tests/Inspector/Http/snapshots/HttpComplexToolSchemaTest-tools_list.json

@@ -48,7 +48,10 @@
               "null"
             ],
             "description": "an optional list of attendee email addresses",
-            "default": null
+            "default": null,
+            "items": {
+              "type": "string"
+            }
           },
           "sendInvites": {
             "type": "boolean",