fix: renumber sets after delete and use last-logged values for prefill

Two bugs fixed:
- Deleting a set left gaps in set numbering (1, 3, 3). Now renumbers
  remaining sets sequentially after deletion.
- Logging set 1 caused the prefill to recalculate via the progression
  engine, shifting suggested reps mid-session. Now prefills from the
  last logged set's actual values; progression suggestion is only used
  for the first set of a session.

app/services/log_service.py

@@ -149,7 +149,8 @@ class LogService:
     def delete_log(self, log_id: int) -> None:
         """Delete a log entry.
 
-        Removes the log and cleans up the parent session if no logs remain.
+        Removes the log, renumbers remaining sets, and cleans up the
+        parent session if no logs remain.
 
         Args:
             log_id: The log entry ID.
@@ -162,15 +163,32 @@ class LogService:
             raise ValueError(f"WorkoutLog with id {log_id} not found")
 
         session_id = log.session_id
+        exercise_id = log.exercise_id
         self._session.delete(log)
         self._session.commit()
         logger.info("log_deleted", log_id=log_id)
 
-        # Clean up orphaned session if no logs remain
+        # Renumber remaining sets so they stay sequential (1, 2, 3...)
         remaining = self._session.exec(
+            select(WorkoutLog)
+            .where(
+                WorkoutLog.session_id == session_id,
+                WorkoutLog.exercise_id == exercise_id,
+            )
+            .order_by(WorkoutLog.set_number)
+        ).all()
+        for i, remaining_log in enumerate(remaining, start=1):
+            if remaining_log.set_number != i:
+                remaining_log.set_number = i
+                self._session.add(remaining_log)
+        if remaining:
+            self._session.commit()
+
+        # Clean up orphaned session if no logs remain for ANY exercise
+        any_remaining = self._session.exec(
             select(WorkoutLog).where(WorkoutLog.session_id == session_id)
         ).first()
-        if remaining is None:
+        if any_remaining is None:
             ws = self._session.get(WorkoutSession, session_id)
             if ws:
                 self._session.delete(ws)