fix(live): cache the oversized-track 502 like other upstream errors (#722)

Keep the new 502, but store it in the 60 s cache as the proxy already does
for 404/429: /tracks/all costs OpenSky credits, so an oversized track must
not be re-downloaded on every reselect. Update the regression test and
credit the fix in CHANGELOG.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+- Aircraft track backfill (`/api/opensky-track`, `/api/adsblol/trace`) now
+  answers 502 when the upstream body exceeds the 5 MB cap, instead of a 200
+  whose error body the client read as an empty track. The failure is cached
+  like other upstream errors, so retries inside the 60 s window do not spend
+  OpenSky credits (Raushankumar0720, #720, #722).
+
 - Saving a key from Provider Settings works again on Macs where Nix or
   Homebrew coreutils sit ahead of `/bin` on `PATH`. The credential hardener
   now spawns Apple's `/bin/chmod -N` by absolute path; GNU `chmod` has no `-N`,