feat(arcrun): implement arcrun MVP — open-source AI workflow engine

Phase 1-5 complete per .agents/specs/u6u-core-mvp/:

**Phase 1 — Cherry-pick & cleanup**
- Create arcrun/ from cypher-executor, credentials, builtins, registry
- Remove 9 InkStone Service Bindings (KBDB, REGISTRY, CLINIC_*, AICEO, MINI_ME)
- Rewrite component-loader: 3-layer (builtin → WASM_BUCKET R2 → error)
- Remove autoPublishMissing.ts, proxy.ts (AICEO), execution-logger.ts (KBDB)
- Clean all KV namespace IDs and InkStone internal URLs from config files

**Phase 2 — contract.yaml completeness**
- Add credentials_required to gmail, google_sheets, telegram, line_notify
- Add config_example to all 21 components with annotated field descriptions

**Phase 3 — Credential injection**
- Add credential-injector.ts: AES-GCM decrypt from CREDENTIALS_KV
- Integrate into GraphExecutor before WASM execution
- Structured errors with repair instructions when credential missing

**Phase 4 — CLI (acr)**
- cli/package.json: arcrun package, bin: acr, deps: commander/js-yaml/chalk/ora
- 8 commands: init, creds push, push, run, validate, parts, list, logs
- Standard mode: writes directly to user's CF KV via CF REST API
- acr init: interactive setup with arcrun.dev API Key registration

**Phase 5 — Open source release prep**
- README.md: 5-minute quickstart, component table, workflow YAML syntax
- CONTRIBUTING.md: TinyGo dev env, component scaffolding, submission flow
- Security audit: no InkStone internal URLs/IDs in committed files
- .gitignore: exclude credentials.yaml, .wrangler, *.wasm

https://claude.ai/code/session_01BnCdSLVH8tUed9VrrPavgT

builtins/src/index.ts

@@ -0,0 +1,27 @@
+// u6u-builtins Worker
+// 所有零件已遷移至 u6u-core/registry/components/ 的 TinyGo .wasm 版本
+// 此 Worker 保留 /init 端點供初始化 Component Registry 使用
+
+import { Hono } from 'hono';
+import { cors } from 'hono/cors';
+import type { Bindings } from './types';
+import { initComponents } from './actions/initComponents';
+
+const app = new Hono<{ Bindings: Bindings }>();
+app.use('*', cors());
+
+app.get('/', c => c.json({
+  service: 'u6u-builtins',
+  version: '2.0.0',
+  status: 'ok',
+  note: '所有零件已遷移至 WASM，請使用 Component Registry',
+}));
+
+// POST /init — 把所有零件上架到 Component Registry（冪等，可重複執行）
+app.post('/init', async c => {
+  const result = await initComponents(c.env);
+  const allOk = result.failed === 0;
+  return c.json({ success: allOk, ...result }, allOk ? 200 : 207);
+});
+
+export default app;