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/@reduxjs/toolkit/dist/uncheckedindexed.ts

@@ -0,0 +1,16 @@
+// inlined from https://github.com/EskiMojo14/uncheckedindexed
+// relies on remaining as a TS file, not .d.ts
+type IfMaybeUndefined<T, True, False> = [undefined] extends [T] ? True : False
+
+const testAccess = ({} as Record<string, 0>)['a']
+
+export type IfUncheckedIndexedAccess<True, False> = IfMaybeUndefined<
+  typeof testAccess,
+  True,
+  False
+>
+
+export type UncheckedIndexedAccess<T> = IfUncheckedIndexedAccess<
+  T | undefined,
+  T
+>