feat(tasks): set up a task that repeats every N days

Add a task gains "Every N days": a length of 2 to 366 days and the date a
cycle began. Editing one keeps its length and start, and "days needed" is
capped at the cycle's length.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/custom-ui.test.tsx

@@ -1296,6 +1296,7 @@ describe("the reader's weekly and monthly tasks in settings", () => {
     const fields = {
       game: "zzz", title: "Activity points", unit: "week" as const, weekday: 1, monthDay: 1,
       kind: "amount" as const, required: "1", target: "2,100", amountUnit: "points",
+      cycleDays: "14", cycleFrom: "",
     };
     expect(taskDraftFrom(fields)).toEqual({
       game: "zzz", title: "Activity points",