Add adapter environment testing infrastructure

Introduce testEnvironment() on ServerAdapterModule with structured
pass/warn/fail diagnostics for all four adapter types (claude_local,
codex_local, process, http). Adds POST test-environment endpoint,
shared types/validators, adapter test implementations, and UI API
client. Includes asset type foundations used by related features.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/adapter-utils/src/index.ts

@@ -5,6 +5,11 @@ export type {
   AdapterExecutionResult,
   AdapterInvocationMeta,
   AdapterExecutionContext,
+  AdapterEnvironmentCheckLevel,
+  AdapterEnvironmentCheck,
+  AdapterEnvironmentTestStatus,
+  AdapterEnvironmentTestResult,
+  AdapterEnvironmentTestContext,
   AdapterSessionCodec,
   AdapterModel,
   ServerAdapterModule,