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/main.go

@@ -0,0 +1,71 @@
+// validate_json — u6u 第一個 WASM 零件
+// 驗證輸入字串是否為合法 JSON 格式
+//
+// 白名單 import（TinyGo 規範）：
+//   - "os"             只用 os.Stdin / os.Stdout
+//   - "io"             io.ReadAll(os.Stdin)
+//   - "encoding/json"  json.Unmarshal / json.Marshal
+//
+// 禁止：goroutine、channel、net/*、os.Open、syscall.*、第三方 module
+//
+// 編譯指令：
+//   tinygo build -o validate_json.wasm -target=wasi .
+//
+// 本地測試：
+//   echo '{"json_string":"{\"key\":\"value\"}"}' | wasmtime validate_json.wasm
+//   echo '{"json_string":"not-json"}' | wasmtime validate_json.wasm
+
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+)
+
+// Input 對應 input_schema
+type Input struct {
+	JSONString string `json:"json_string"`
+}
+
+// Output 對應 output_schema
+type Output struct {
+	Valid bool   `json:"valid"`
+	Error string `json:"error,omitempty"`
+}
+
+func main() {
+	// 1. 讀取 stdin
+	raw, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		writeOutput(Output{Valid: false, Error: "failed to read stdin: " + err.Error()})
+		return
+	}
+
+	// 2. 解析 input JSON
+	var input Input
+	if err := json.Unmarshal(raw, &input); err != nil {
+		writeOutput(Output{Valid: false, Error: "invalid input JSON: " + err.Error()})
+		return
+	}
+
+	// 3. 驗證 json_string 欄位
+	if input.JSONString == "" {
+		writeOutput(Output{Valid: false, Error: "json_string is required"})
+		return
+	}
+
+	// 4. 嘗試解析 json_string
+	var target interface{}
+	if err := json.Unmarshal([]byte(input.JSONString), &target); err != nil {
+		writeOutput(Output{Valid: false, Error: err.Error()})
+		return
+	}
+
+	writeOutput(Output{Valid: true})
+}
+
+func writeOutput(out Output) {
+	data, _ := json.Marshal(out)
+	os.Stdout.Write(data)
+}