feat(workspaces): tile stat line shows months instead of a short date

The relative last-activity time switched to an MM/DD date once past a week.
Now it stays relative: days continue to a month (30 days), then months
("10d", "29d", "1mo", "2mo", ...). A month ≈ 30 days; the label never
becomes an absolute date.

Verification: svelte-check 0 errors/0 warnings; vitest 1694/1694; biome
clean on touched files; build ok.

2 files changed, 13 insertions, 10 deletions

diff --git a/src/features/workspaces/logic/view-model.test.ts b/src/features/workspaces/logic/view-model.test.ts
index d283481..d13f485 100644
--- a/src/features/workspaces/logic/view-model.test.ts
+++ b/src/features/workspaces/logic/view-model.test.ts
@@ -49,10 +49,15 @@ describe("relativeTime", () => {
     expect(relativeTime(now - 3 * 24 * 60 * 60_000, now)).toBe("3d");
   });
 
-  it("is a short date beyond a week", () => {
-    // 7+ days ago: just check it is a MM/DD string.
-    const s = relativeTime(now - 10 * 24 * 60 * 60_000, now);
-    expect(s).toMatch(/^\d{2}\/\d{2}$/);
+  it("keeps days past a week (no short date) up to a month", () => {
+    expect(relativeTime(now - 10 * 24 * 60 * 60_000, now)).toBe("10d");
+    expect(relativeTime(now - 29 * 24 * 60 * 60_000, now)).toBe("29d");
+  });
+
+  it("is months past a month", () => {
+    expect(relativeTime(now - 30 * 24 * 60 * 60_000, now)).toBe("1mo");
+    expect(relativeTime(now - 75 * 24 * 60 * 60_000, now)).toBe("2mo");
+    expect(relativeTime(now - 365 * 24 * 60 * 60_000, now)).toBe("12mo");
   });
 });
 
diff --git a/src/features/workspaces/logic/view-model.ts b/src/features/workspaces/logic/view-model.ts
index 0b9f239..6f5a635 100644
--- a/src/features/workspaces/logic/view-model.ts
+++ b/src/features/workspaces/logic/view-model.ts
@@ -96,10 +96,8 @@ export function relativeTime(then: number, now: number): string {
   const hours = Math.floor(mins / 60);
   if (hours < 24) return `${hours}h`;
   const days = Math.floor(hours / 24);
-  if (days < 7) return `${days}d`;
-  // Beyond a week: a short date (MM/DD). Uses UTC parts for determinism in tests.
-  const d = new Date(then);
-  const month = String(d.getUTCMonth() + 1).padStart(2, "0");
-  const day = String(d.getUTCDate()).padStart(2, "0");
-  return `${month}/${day}`;
+  if (days < 30) return `${days}d`;
+  // Past a month: months (a month ≈ 30 days). No short date — the label
+  // stays relative forever.
+  return `${Math.floor(days / 30)}mo`;
 }