docs(changelog): record #600 in the 3.5.0 section

#600 merged into main while the release PR was open, so the 3.5.0 section
went in without it. Nothing in that PR touched the CHANGELOG, and no check
covers "everything merged since the last tag is written down", so tagging
v3.5.0 as main stands would ship the standings-endpoint fix undocumented.

The entry goes under Sports data, next to the other ESPN fetch changes, and
is written from the commit: what the old order did, why a college league's
200 defeated the 404 fallback, and what is now treated as routine.

No version change: 3.5.0 is not tagged yet, so this belongs in that section
rather than a new one. `scripts/check_release_version.py v3.5.0` still passes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Rqzd6Nz2bQJp5K7DD5dS4X

CHANGELOG.md

@@ -125,6 +125,19 @@ New modules a plugin may import via `src.*` (floor on 3.5.0):
   fetched, which keeps the peak memory of a four-capped-month fetch to about
   16 MB over the sequential path rather than 43 MB — `docs/LOW_MEMORY_BOARDS.md`
   puts a 1 GB Pi 3B+ at under 200 MB of headroom.
+- `ESPNDataSource.fetch_standings` asks each league the endpoint that league
+  actually publishes. It tried `/standings` first whatever the league and fell
+  back to `/rankings` only on a 404, but college leagues answer `/standings`
+  with a 200 that carries no poll, so the fallback never fired: the rank badge
+  simply never appeared and anything keyed off rankings quietly did nothing.
+  Endpoints are now ordered by whether the league publishes a poll, and a 200
+  that lacks the key counts as a miss, so a league answering both still ends up
+  with whichever carries the poll. Only a 404 is routine — that is how a league
+  says it has none; a connection error, a timeout or an unparseable body is
+  logged as an error again, and a bug raised while inspecting the payload is no
+  longer swallowed as a missing poll. This is the implementation the football,
+  baseball and hockey boards already ship; core was the last copy on the old
+  one.
 
 ### Scrolling