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/merge/component.contract.yaml

@@ -0,0 +1,50 @@
+canonical_id: "merge"
+display_name: "合併物件"
+category: "logic"
+version: "v1"
+wasi_target: "preview1"
+stability: "floating"
+runtime_compat:
+  - "cf-workers"
+  - "workerd"
+  - "wazero"
+constraints:
+  max_size_kb: 2048
+  max_cold_start_ms: 50
+  no_network_syscall: true
+  no_filesystem_syscall: true
+  io_model: "stdin_stdout_json"
+input_schema:
+  type: object
+  required: [inputs]
+  properties:
+    inputs:
+      type: array
+      description: 要合併的物件陣列，後者欄位覆蓋前者
+      items:
+        type: object
+output_schema:
+  type: object
+  properties:
+    success:
+      type: boolean
+    data:
+      type: object
+      description: 所有輸入物件合併後的結果
+gherkin_tests:
+  - scenario: "合併兩個物件"
+    given: '{"inputs":[{"a":1},{"b":2}]}'
+    then_contains: '"a":1'
+  - scenario: "後者欄位覆蓋前者"
+    given: '{"inputs":[{"a":1},{"a":2}]}'
+    then_contains: '"a":2'
+  - scenario: "inputs 為空陣列時失敗"
+    given: '{"inputs":[]}'
+    then_contains: '{"success":false'
+tags: [builtin, merge, combine, object, context]
+description: "將多個物件合併為一個，後者欄位覆蓋前者同名欄位。"
+config_example: |
+  my_merge:                               # 節點名稱（可自訂）
+    inputs:                               # 要合併的物件陣列（必填）
+      - "{{node_a.data}}"                 # 第一個來源物件
+      - "{{node_b.data}}"                 # 第二個來源物件（後者覆蓋前者同名欄位）

registry/components/merge/go.mod

@@ -0,0 +1,3 @@
+module component
+
+go 1.21

registry/components/merge/main.go

@@ -0,0 +1,44 @@
+// merge — 合併多個輸入物件為一個
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+)
+
+type Input struct {
+	Inputs []map[string]interface{} `json:"inputs"`
+}
+
+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 len(input.Inputs) == 0 {
+		writeError("inputs 陣列不能為空")
+		return
+	}
+
+	result := make(map[string]interface{})
+	for _, obj := range input.Inputs {
+		for k, v := range obj {
+			result[k] = v
+		}
+	}
+
+	out, _ := json.Marshal(map[string]interface{}{"success": true, "data": result})
+	os.Stdout.Write(out)
+}
+
+func writeError(msg string) {
+	out, _ := json.Marshal(map[string]interface{}{"success": false, "error": msg})
+	os.Stdout.Write(out)
+}