feat(recurring): datable cancellation via an "Ends" column

Gap 2 (spec §10): endedFrom is typed as any IsoDate and the spec calls it
"cancellation", but Settings only ever wrote currentMonth — backdating or
forward-dating a cancellation was import-only.

Add an "Ends" column beside "Starts" in the Recurring costs table, edited and
validated the same way (isValidEndedFrom — no granularity rule, per §10, but
still refuses a calendar-impossible date like "2026-02-30"). Empty means "not
ended" and clears the cancellation.

Coherence rule: `archived` mirrors "endedFrom is set". setRecurringCostEndedFrom
is the one place that now enforces it — endRecurringCost and
restoreRecurringCost (the one-click row buttons) delegate to it, so the column
and the buttons can never leave a bill dimmed-but-live or ended-but-undimmed.

Also closes the same calendar-impossible gap in the JSON importer, which
checked endedFrom's shape but not its calendar validity, unlike startDate.

src/export/json.test.ts

@@ -302,6 +302,27 @@ describe("recurring cost validation", () => {
       .toThrow(/ended-from date/);
   });
 
+  // Same residual-C1 gap as startDate: PURCHASE_DATE checks shape and digit
+  // range, not calendar validity, so "2026-02-30" passes it. §10: endedFrom
+  // carries no granularity rule, but it must still be a real date.
+  test("a calendar-impossible endedFrom is refused (day- or month-shaped)", () => {
+    expect(() => parseDatasetJson(withRecurring([{ ...valid, endedFrom: "2026-02-30" }])))
+      .toThrow(/calendar-impossible ended-from/);
+    expect(() => parseDatasetJson(withRecurring([{ ...valid, endedFrom: "2026-02-29" }]))) // not a leap year
+      .toThrow(/calendar-impossible ended-from/);
+  });
+
+  test("a valid endedFrom of either granularity is accepted, regardless of recurrence kind", () => {
+    expect(
+      parseDatasetJson(withRecurring([{ ...valid, endedFrom: "2026-06" }])).recurring.length,
+    ).toBe(1);
+    expect(
+      parseDatasetJson(
+        withRecurring([{ ...valid, endedFrom: "2026-06-17" }]), // month-only recurrence, day-granular end
+      ).recurring.length,
+    ).toBe(1);
+  });
+
   test("an interval below 1 is refused, not clamped", () => {
     // Clamping would silently change the bill's schedule. The walk in
     // occurrences.ts cannot terminate without this.