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

registry/components/validate_json/README.md

@@ -0,0 +1,42 @@
+# validate_json
+
+u6u 第一個 WASM 零件。驗證輸入字串是否為合法 JSON 格式。
+
+## 編譯
+
+需要安裝 [TinyGo](https://tinygo.org/getting-started/install/)：
+
+```bash
+# macOS
+brew install tinygo
+
+# 編譯為 WASM
+tinygo build -o validate_json.wasm -target=wasi .
+```
+
+## 本地測試
+
+```bash
+# 合法 JSON → {"valid":true}
+echo '{"json_string":"{\"key\":\"value\"}"}' | wasmtime validate_json.wasm
+
+# 非法 JSON → {"valid":false,"error":"..."}
+echo '{"json_string":"not-json"}' | wasmtime validate_json.wasm
+
+# 空字串 → {"valid":false,"error":"json_string is required"}
+echo '{"json_string":""}' | wasmtime validate_json.wasm
+```
+
+## 提交至 Component Registry
+
+```bash
+# 驗證合約格式
+curl -X POST https://component-registry.finally.click/components/validate-contract \
+  -H "Content-Type: application/json" \
+  -d @component.contract.yaml
+
+# 提交零件（multipart）
+curl -X POST https://component-registry.finally.click/components \
+  -F "contract=@component.contract.yaml;type=application/yaml" \
+  -F "wasm=@validate_json.wasm;type=application/wasm"
+```