fix: strictly validate manifests (#66)

* fix: strictly validate manifests

* spec: align tests with strict schema

test/schemas.test.ts

@@ -65,15 +65,11 @@ describe("DxtManifestSchema", () => {
           args: ["main.py"],
           env: { PYTHONPATH: "." },
         },
-        runtime_requirements: {
-          python: ">=3.8",
-        },
       },
       tools: [
         {
           name: "my_tool",
           description: "A useful tool",
-          input_schema: { type: "object" },
         },
       ],
       keywords: ["test", "example"],
@@ -86,13 +82,6 @@ describe("DxtManifestSchema", () => {
           node: ">=16.0.0",
         },
       },
-      settings: {
-        configurable: true,
-        schema: {
-          type: "object",
-          properties: {},
-        },
-      },
       user_config: {
         api_key: {
           type: "string",