feat: add landing page + builtins Worker + BETA_TEST guide + README

- landing/: Next.js 15 app for arcrun.dev (dashboard, integrations,
  API docs, login). Deploys via Cloudflare Pages — CI scan skips
  this via pages_build_output_dir marker.
- builtins/: minimal Hono Worker at arcrun-builtins (/init for
  one-shot component registry seeding). initComponents logic is
  flagged stale in src/index.ts for future rewrite.
- BETA_TEST.md: pre-launch validation playbook.
- README.md: updated to match current arcrun.dev / acr CLI flow.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

builtins/src/actions/initComponents.ts

@@ -0,0 +1,43 @@
+// initComponents：把所有內建零件上架到 Component Registry（via Service Binding）
+import type { Bindings } from '../types';
+import { buildComponentDefs } from '../types';
+
+async function publishOne(
+  registry: Fetcher,
+  def: ReturnType<typeof buildComponentDefs>[number],
+): Promise<{ id: string; status: number; ok: boolean; error?: unknown }> {
+  const payload = {
+    id: def.id,
+    name: def.name,
+    description: def.description,
+    url: def.url,
+    method: def.method,
+    tags: def.tags,
+    input_schema: JSON.stringify(def.input_schema),
+    output_schema: JSON.stringify(def.output_schema),
+    author: 'u6u-builtins',
+    version: '1.0.0',
+  };
+
+  const res = await registry.fetch('http://registry/components', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(payload),
+  });
+
+  const body = await res.json().catch(() => ({ error: 'parse error' }));
+  // 201 = 新建成功；409 = 已存在（也算 ok）
+  const isOk = res.status === 201 || res.status === 409 || res.ok;
+  return { id: def.id, status: res.status, ok: isOk, ...(!isOk && { error: body }) };
+}
+
+export async function initComponents(
+  env: Bindings,
+): Promise<{ ok: number; failed: number; results: unknown[] }> {
+  const defs = buildComponentDefs(env.WORKER_BASE_URL);
+  const results = await Promise.all(defs.map(def => publishOne(env.REGISTRY, def)));
+
+  const ok = results.filter(r => r.ok).length;
+  const failed = results.filter(r => !r.ok).length;
+  return { ok, failed, results };
+}