Add settings page for managing forecasting API key and URL via UI

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/node_modules/jsonfile/utils.js

@@ -0,0 +1,18 @@
+function stringify (obj, { EOL = '\n', finalEOL = true, replacer = null, spaces } = {}) {
+  const EOF = finalEOL ? EOL : ''
+  const str = JSON.stringify(obj, replacer, spaces)
+
+  if (str === undefined) {
+    throw new TypeError(`Converting ${typeof obj} value to JSON is not supported`)
+  }
+
+  return str.replace(/\n/g, EOL) + EOF
+}
+
+function stripBom (content) {
+  // we do this because JSON.parse would convert it to a utf8 string if encoding wasn't specified
+  if (Buffer.isBuffer(content)) content = content.toString('utf8')
+  return content.replace(/^\uFEFF/, '')
+}
+
+module.exports = { stringify, stripBom }