chore: auto-commit (57 archivos)

- frontend/functions/core/format_datetime_short.md
- frontend/functions/core/format_datetime_short.test.ts
- frontend/functions/core/format_datetime_short.ts
- frontend/functions/core/format_duration.md
- frontend/functions/core/format_duration.test.ts
- frontend/functions/core/format_duration.ts
- frontend/functions/core/month_grid.md
- frontend/functions/core/month_grid.test.ts
- frontend/functions/core/month_grid.ts
- frontend/functions/core/string_hash_palette.md
- ...

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/functions/infra/fetch_json.ts

@@ -0,0 +1,44 @@
+/**
+ * HTTPError — error HTTP con status code.
+ * Lanzado por fetchJSON cuando la respuesta no es ok.
+ */
+export class HTTPError extends Error {
+  constructor(public status: number, message: string) {
+    super(message);
+    this.name = "HTTPError";
+  }
+}
+
+/**
+ * fetchJSON — wrapper de fetch que parsea JSON, lanza HTTPError en errores HTTP
+ * y retorna undefined en 204 No Content.
+ *
+ * URL final: `${baseUrl ?? ""}${path}`.
+ * Headers default: `{ "Content-Type": "application/json" }`, mergeables via init.headers.
+ * credentials: "include" por defecto, sobreescribible via init.
+ */
+export async function fetchJSON<T>(
+  path: string,
+  init?: RequestInit,
+  baseUrl?: string,
+): Promise<T> {
+  const res = await fetch(`${baseUrl ?? ""}${path}`, {
+    credentials: "include",
+    ...init,
+    headers: {
+      "Content-Type": "application/json",
+      ...(init?.headers ?? {}),
+    },
+  });
+
+  if (!res.ok) {
+    const err = await res.json().catch(() => ({ Message: res.statusText }));
+    throw new HTTPError(
+      res.status,
+      err.Message ?? err.message ?? res.statusText,
+    );
+  }
+
+  if (res.status === 204) return undefined as T;
+  return res.json() as Promise<T>;
+}