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/string_ops/main.go

@@ -0,0 +1,116 @@
+// string_ops — 字串操作
+// 支援: upper, lower, trim, capitalize, replace, split, join, includes,
+//        starts_with, ends_with, length, substring
+//
+//go:build tinygo
+
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+	"strings"
+)
+
+type Args struct {
+	From   string   `json:"from"`
+	To     string   `json:"to"`
+	Sep    string   `json:"sep"`
+	Items  []string `json:"items"`
+	Substr string   `json:"substr"`
+	Prefix string   `json:"prefix"`
+	Suffix string   `json:"suffix"`
+	Start  int      `json:"start"`
+	End    int      `json:"end"`
+}
+
+type Input struct {
+	Operation string `json:"operation"`
+	Input     string `json:"input"`
+	Args      Args   `json:"args"`
+}
+
+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.Operation == "" {
+		writeError("operation 必填")
+		return
+	}
+
+	var result interface{}
+
+	switch input.Operation {
+	case "upper":
+		result = strings.ToUpper(input.Input)
+	case "lower":
+		result = strings.ToLower(input.Input)
+	case "trim":
+		result = strings.TrimSpace(input.Input)
+	case "capitalize":
+		if len(input.Input) == 0 {
+			result = ""
+		} else {
+			result = strings.ToUpper(input.Input[:1]) + strings.ToLower(input.Input[1:])
+		}
+	case "replace":
+		result = strings.ReplaceAll(input.Input, input.Args.From, input.Args.To)
+	case "split":
+		sep := input.Args.Sep
+		if sep == "" {
+			sep = ","
+		}
+		result = strings.Split(input.Input, sep)
+	case "join":
+		sep := input.Args.Sep
+		result = strings.Join(input.Args.Items, sep)
+	case "includes":
+		result = strings.Contains(input.Input, input.Args.Substr)
+	case "starts_with":
+		result = strings.HasPrefix(input.Input, input.Args.Prefix)
+	case "ends_with":
+		result = strings.HasSuffix(input.Input, input.Args.Suffix)
+	case "length":
+		result = len([]rune(input.Input))
+	case "substring":
+		runes := []rune(input.Input)
+		start := input.Args.Start
+		end := input.Args.End
+		if start < 0 {
+			start = 0
+		}
+		if end <= 0 || end > len(runes) {
+			end = len(runes)
+		}
+		if start > end {
+			start = end
+		}
+		result = string(runes[start:end])
+	default:
+		writeError("不支援的 operation: " + input.Operation)
+		return
+	}
+
+	out, _ := json.Marshal(map[string]interface{}{
+		"success": true,
+		"data": map[string]interface{}{
+			"result":    result,
+			"operation": input.Operation,
+		},
+	})
+	os.Stdout.Write(out)
+}
+
+func writeError(msg string) {
+	out, _ := json.Marshal(map[string]interface{}{"success": false, "error": msg})
+	os.Stdout.Write(out)
+}