feat(node-go): add golangci-lint + Renovate auto-bump

- Add golangci-lint v2.12.2 to node-go image (arch-aware via official install.sh)
- Wire renovate.json to auto-bump GOLANGCI_LINT_VERSION (minor/patch automerge)
  and GO_VERSION (patch automerge); keep pins for reproducible/rollback-able builds
- Add node-go/README.md documenting installed tools and what's NOT included
- Update root README accordingly

Co-Authored-By: Claude <noreply@anthropic.com>

renovate.json

@@ -1,3 +1,36 @@
 {
-  "$schema": "https://docs.renovatebot.com/renovate-schema.json"
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "customManagers": [
+    {
+      "customType": "regex",
+      "description": "Bump golangci-lint version ARG trong node-go/Dockerfile",
+      "fileMatch": ["node-go/Dockerfile$"],
+      "matchStrings": ["ARG GOLANGCI_LINT_VERSION=(?<currentValue>\\S+)"],
+      "datasourceTemplate": "github-releases",
+      "depNameTemplate": "golangci/golangci-lint"
+    },
+    {
+      "customType": "regex",
+      "description": "Bump Go version ARG trong node-go/Dockerfile",
+      "fileMatch": ["node-go/Dockerfile$"],
+      "matchStrings": ["ARG GO_VERSION=(?<currentValue>\\S+)"],
+      "datasourceTemplate": "golang-version",
+      "depNameTemplate": "go"
+    }
+  ],
+  "packageRules": [
+    {
+      "description": "golangci-lint: auto-merge minor/patch, major (vd v2->v3) can review",
+      "matchDatasources": ["github-releases"],
+      "matchPackageNames": ["golangci/golangci-lint"],
+      "matchUpdateTypes": ["minor", "patch"],
+      "automerge": true
+    },
+    {
+      "description": "Go: chi auto-merge patch; minor (vd 1.26->1.27) can review thu cong",
+      "matchDatasources": ["golang-version"],
+      "matchUpdateTypes": ["patch"],
+      "automerge": true
+    }
+  ]
 }