fix(sports): drop capped month payloads before fetching their days

Review of the concurrent chunk fetch found it raised the worst-case peak
memory more than the concurrency explains. The old loop discarded a month
that came back at the 500-event cap the moment it saw it; the rewrite kept
every capped month alive in `results`/`slots` until all of their day
requests had finished.

Measured on a Pi 4 fetching 20260201-20260531 college baseball (four capped
months, 5462 events), peak RSS growth over the call:

  sequential (main)               83 MB
  concurrent, months retained    121 MB  (+43)
  concurrent, one worker         108 MB  -- the retention alone was +25
  concurrent, months dropped      98-100 MB (+16)

docs/LOW_MEMORY_BOARDS.md puts a 1 GB Pi 3B+ at under 200 MB of headroom,
where running out makes the board unreachable until a power cycle, so the
difference matters. The remaining +16 MB is six responses parsing at once;
three workers saved about 6 MB more, within run-to-run noise, so the worker
count stays at six.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/common/espn_dates.py

@@ -272,9 +272,10 @@ def fetch_espn_date_chunks(
 
     # A month that came back at the cap is truncated; its days replace it in
     # place, so merged events stay in chunk order however the requests raced.
-    slots: List[Any] = list(results)
+    slots: List[Any] = results
     capped: Dict[int, List[str]] = {}
-    for index, (chunk, payload) in enumerate(zip(chunks, results)):
+    for index, chunk in enumerate(chunks):
+        payload = slots[index]
         if payload is None or len(chunk) != 6:
             continue
         events = payload.get("events") if isinstance(payload, dict) else None
@@ -285,6 +286,13 @@ def fetch_espn_date_chunks(
                     chunk, ESPN_MAX_LIMIT,
                 )
             capped[index] = _days_of_month(chunk)
+            # Drop the truncated month now rather than after its days arrive:
+            # a capped college-baseball month is ~2MB of parsed JSON, and
+            # holding four of them through ~120 day requests added ~25MB to
+            # the peak -- more than the concurrency itself. Low-memory boards
+            # (docs/LOW_MEMORY_BOARDS.md) have under 200MB of headroom.
+            slots[index] = None
+    payload = events = None
 
     if capped:
         days = [day for index in sorted(capped) for day in capped[index]]