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.

config/runtime/staging.json

@@ -14,6 +14,7 @@
     "SERVICE_WORKER": "DEFAULT",
     "OFFLINE_COMMANDS": "DEFAULT"
   },
+  "TECH_LOG_STUDIO_SOURCE": "HTTP",
   "FEATURE_OVERRIDES": {
     "reference-feature": "DEFAULT"
   }