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

builtins/wrangler.toml

@@ -0,0 +1,26 @@
+name = "arcrun-builtins"
+main = "src/index.ts"
+compatibility_date = "2025-02-19"
+compatibility_flags = ["nodejs_compat"]
+workers_dev = true
+
+# Service Binding：呼叫 Cypher Executor 執行排程工作流
+[[services]]
+binding = "CYPHER"
+service = "arcrun-cypher-executor"   # 填入你的 cypher-executor Worker 名稱
+
+# KV Store：cron: 前綴 = 排程定義，ai-transform: 前綴 = 編譯後轉換函式
+[[kv_namespaces]]
+binding = "U6U_STORE"
+id = ""   # 填入你的 KV Namespace ID
+
+# Workers AI：ai-transform 零件的 compile 階段使用
+[ai]
+binding = "AI"
+
+# Cron Trigger：每分鐘掃描並執行到期的排程工作流
+[triggers]
+crons = ["* * * * *"]
+
+[vars]
+ENVIRONMENT = "production"