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.

src/contracts/env.ts

@@ -49,6 +49,9 @@ export const ENV_REGISTRY = Object.freeze({
   CAPABILITY_OVERRIDES: runtime("public", false, null),
   // §3.5: likewise for features — subtractive, keyed by installed feature id.
   FEATURE_OVERRIDES: runtime("public", false, null),
+  // TechLog Studio gateway adapter selection. Defaults to MOCK while the
+  // backend does not exist yet.
+  TECH_LOG_STUDIO_SOURCE: runtime("public", false, "MOCK"),
   // §3.5: build-time narrowing of the product manifest. A feature left out
   // here is not imported by any registry and never reaches the bundle.
   VITE_PRODUCT_FEATURES: build("compile-time", false, null),