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/ai_transform_compile/main.go

@@ -0,0 +1,53 @@
+// ai_transform_compile — 接收自然語言描述，輸出 transform stub
+// Phase 0: 輸出 placeholder，Phase 2 再接 AI host function
+//
+//go:build tinygo
+
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+	"strconv"
+	"time"
+)
+
+type Input struct {
+	Description  string          `json:"description"`
+	ExampleInput json.RawMessage `json:"example_input"`
+}
+
+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.Description == "" {
+		writeError("description 必填")
+		return
+	}
+
+	transformID := "at-" + strconv.FormatInt(time.Now().UnixNano()/1e6, 10)
+
+	out, _ := json.Marshal(map[string]interface{}{
+		"success": true,
+		"data": map[string]interface{}{
+			"transform_id": transformID,
+			"fn_preview":   "// AI generated\n// TODO: Phase 2 will implement AI-powered code generation\nreturn input;",
+			"description":  input.Description,
+		},
+	})
+	os.Stdout.Write(out)
+}
+
+func writeError(msg string) {
+	out, _ := json.Marshal(map[string]interface{}{"success": false, "error": msg})
+	os.Stdout.Write(out)
+}