feat: select the TechLog Studio adapter from runtime configuration

Adds TECH_LOG_STUDIO_SOURCE (MOCK | HTTP, default MOCK) to the V2 runtime
config schema so a build can switch createTechLogFeatureInstalledInput
between the mock and HTTP Studio gateways without a rebuild. V1 documents
predate the key and always normalize to MOCK. The HTTP gateway is
constructed with only { operations } per Task 4's actual signature -
no CSRF provider is wired here; that lands with attachCredentials at a
later composition-root task.

Updates every existing Studio test call site to the new required
createTechLogFeatureInstalledInput(context) signature via a shared
tests/helpers/studio-install-context.ts MOCK fixture, so the whole
existing Studio suite keeps exercising the mock adapter unchanged.

tests/features/tech-log/runtime-composition.test.ts

@@ -32,8 +32,11 @@ function inputOf(document: WorkingCopy) {
   return input;
 }
 
-function installedInputs(): InstalledInputs {
+function installedInputs(
+  studioSource: "MOCK" | "HTTP" = "MOCK",
+): InstalledInputs {
   return createInstalledFeatureInputs({
+    studioSource,
     contractOperations: {
       async execute() {
         throw new Error("reference executor is not used by composition tests");
@@ -59,6 +62,16 @@ test("installs TechLog beside the retained reference feature through application
   );
 });
 
+test("selects the mock gateway by default and the HTTP gateway when switched", async () => {
+  const mockGateway = installedInputs("MOCK")["tech-log"].createStudioGateway();
+  const httpGateway = installedInputs("HTTP")["tech-log"].createStudioGateway();
+
+  // The mock reads an in-memory fixture immediately. HTTP defers to the
+  // (here, throwing) contract executor, so it rejects instead.
+  await assert.doesNotReject(mockGateway.getDashboard());
+  await assert.rejects(httpGateway.getDashboard());
+});
+
 test("each createStudioGateway call owns an isolated mutable Studio session", async () => {
   const installed = installedInputs();
   const first = installed["tech-log"].createStudioGateway();