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/http_request/main.go

@@ -0,0 +1,100 @@
+// http_request — 發送任意 HTTP 請求，回傳 status + body
+// 透過 host function 發出 HTTP，.wasm 本身不含網路 syscall
+//
+//go:build tinygo
+
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+	"unsafe"
+)
+
+// host function 宣告（由 WASI shim 注入）
+//
+//go:wasmimport u6u http_request
+func hostHttpRequest(
+	urlPtr uintptr, urlLen uint32,
+	methodPtr uintptr, methodLen uint32,
+	headersPtr uintptr, headersLen uint32,
+	bodyPtr uintptr, bodyLen uint32,
+	outPtr uintptr, outLenPtr uintptr,
+) uint32
+
+type Input struct {
+	URL     string          `json:"url"`
+	Method  string          `json:"method"`
+	Headers map[string]string `json:"headers"`
+	Body    json.RawMessage `json:"body"`
+}
+
+func main() {
+	raw, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		writeError("failed to read stdin: " + err.Error())
+		return
+	}
+	var input Input
+	if err := json.Unmarshal(raw, &input); err != nil {
+		writeError("invalid input JSON: " + err.Error())
+		return
+	}
+	if input.URL == "" {
+		writeError("url 必填")
+		return
+	}
+
+	method := input.Method
+	if method == "" {
+		method = "GET"
+	}
+
+	// 序列化 headers
+	headersJSON := "{}"
+	if len(input.Headers) > 0 {
+		b, _ := json.Marshal(input.Headers)
+		headersJSON = string(b)
+	}
+
+	// body
+	bodyStr := ""
+	if len(input.Body) > 0 {
+		bodyStr = string(input.Body)
+	}
+
+	// 呼叫 host function
+	urlBytes := []byte(input.URL)
+	methodBytes := []byte(method)
+	headersBytes := []byte(headersJSON)
+	bodyBytes := []byte(bodyStr)
+
+	outBuf := make([]byte, 65536) // 64KB output buffer
+	var outLen uint32
+
+	result := hostHttpRequest(
+		uintptr(unsafe.Pointer(&urlBytes[0])), uint32(len(urlBytes)),
+		uintptr(unsafe.Pointer(&methodBytes[0])), uint32(len(methodBytes)),
+		uintptr(unsafe.Pointer(&headersBytes[0])), uint32(len(headersBytes)),
+		uintptr(unsafe.Pointer(&bodyBytes[0])), uint32(len(bodyBytes)),
+		uintptr(unsafe.Pointer(&outBuf[0])), uintptr(unsafe.Pointer(&outLen)),
+	)
+
+	if result != 0 {
+		writeError("HTTP request failed")
+		return
+	}
+
+	responseStr := string(outBuf[:outLen])
+	out, _ := json.Marshal(map[string]interface{}{
+		"success": true,
+		"data":    map[string]interface{}{"body": responseStr},
+	})
+	os.Stdout.Write(out)
+}
+
+func writeError(msg string) {
+	out, _ := json.Marshal(map[string]interface{}{"success": false, "error": msg})
+	os.Stdout.Write(out)
+}