feat: unify task and habit pages with Today

frontend/src/lib/task-open-total.ts

@@ -0,0 +1,13 @@
+type OpenTotalPayload = { total?: number; items?: unknown[] }
+
+export function loadTaskOpenTotal(
+  request: () => Promise<OpenTotalPayload>,
+  isCurrent: () => boolean,
+  commit: (value: number) => void,
+) {
+  void request()
+    .then((data) => {
+      if (isCurrent()) commit(Number(data.total ?? data.items?.length ?? 0))
+    })
+    .catch(() => { /* Summary failure is intentionally non-fatal. */ })
+}