fix(workouts): refuse a manual workout that would end in the future

The form's start defaults to the minute it opened, so a workout logged
right after it finished was stored as ending up to a day ahead. The
duration now fails validation when start + duration lies past now, with
the same one-minute slack the start check uses.

src/lib/workouts/__tests__/manual-entry.test.ts

@@ -136,9 +136,9 @@ describe("buildManualWorkoutEntry — validation", () => {
   });
 
   it("tolerates the minute the form was opened in", () => {
-    // 14:00:30 Berlin is 30 s past `now`: inside the slack.
+    // 13:15 Berlin + 45 min ends at 12:00Z, 30 s past `now`: inside the slack.
     const result = buildManualWorkoutEntry(
-      draft({ start: "2026-09-15T14:00" }),
+      draft({ start: "2026-09-15T13:15" }),
       {
         ...CTX,
         now: new Date("2026-09-15T11:59:30Z"),
@@ -147,6 +147,13 @@ describe("buildManualWorkoutEntry — validation", () => {
     expect(result.ok).toBe(true);
   });
 
+  it("refuses a workout that would end in the future", () => {
+    // Logged at 14:00 Berlin with the start left at 13:30: 45 min ends 14:15.
+    expect(errorsOf({ start: "2026-09-15T13:30" }).duration).toBe(
+      "insights.workouts.manual.errors.endInFuture",
+    );
+  });
+
   it("asks for a start", () => {
     expect(errorsOf({ start: "" }).start).toBe(
       "insights.workouts.manual.errors.startRequired",

src/lib/workouts/manual-entry.ts

@@ -235,6 +235,18 @@ function manualWorkoutSchema(ctx: ManualWorkoutContext) {
             path: ["duration"],
             message: `${ERR}.durationTooLong`,
           });
+        } else if (
+          // The default start is "now", so a workout logged right after it
+          // finished would otherwise be stored as ending in the future.
+          startedAt !== null &&
+          startedAt.getTime() + sec * 1000 >
+            ctx.now.getTime() + FUTURE_TOLERANCE_MS
+        ) {
+          issue.addIssue({
+            code: "custom",
+            path: ["duration"],
+            message: `${ERR}.endInFuture`,
+          });
         }
       }