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/adapters/codex-local/src/server/index.ts

@@ -1,4 +1,5 @@
 export { execute } from "./execute.js";
+export { testEnvironment } from "./test.js";
 export { parseCodexJsonl, isCodexUnknownSessionError } from "./parse.js";
 import type { AdapterSessionCodec } from "@paperclip/adapter-utils";