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/shared/src/validators/asset.ts

@@ -0,0 +1,14 @@
+import { z } from "zod";
+
+export const createAssetImageMetadataSchema = z.object({
+  namespace: z
+    .string()
+    .trim()
+    .min(1)
+    .max(120)
+    .regex(/^[a-zA-Z0-9/_-]+$/)
+    .optional(),
+});
+
+export type CreateAssetImageMetadata = z.infer<typeof createAssetImageMetadataSchema>;
+