policies: add standard policy files, linting, formatting

- Add .editorconfig, .eslintrc.json, .prettierrc, .prettierignore, .dockerignore, .gitignore
- Add Makefile with lint, fmt, fmt-check, secret-scan, test (skip) targets
- Add package.json with eslint@^8.56.0, eslint-plugin-security, prettier
- Add tools/secret-scan.sh
- Fix unused variable (fs -> _fs)
- Auto-format with prettier
- make check passes clean (0 errors, 11 warnings)

package.json

@@ -0,0 +1,11 @@
+{
+  "name": "mattermost-openclaw-livestatus",
+  "version": "1.0.0",
+  "private": true,
+  "description": "OpenClaw Live Status Tool for Mattermost",
+  "devDependencies": {
+    "eslint": "^8.56.0",
+    "eslint-plugin-security": "^2.1.0",
+    "prettier": "^3.2.0"
+  }
+}