fix(error-classifier): don't misclassify unsupported-param 400s as context overflow

A GPT-5 model rejecting max_tokens returns a 400 whose message contains the
literal substring 'max_tokens' — one of the _CONTEXT_OVERFLOW_PATTERNS. The 400
path in _classify_400 checked overflow patterns before any request-validation
check (which only existed on the 5xx path), so the parameter error was routed
into the compression loop, re-sent with the same bad param, and ended in
'Cannot compress further' on a tiny context.

Hoist a request-validation guard (unsupported/unknown parameter) above the
context-overflow check in _classify_400. Deliberately excludes the generic
invalid_request_error code, which OpenAI also stamps on real overflow 400s, so
genuine overflows still compress. Pairs with the max_completion_tokens param
fix that stops the bad request at the source.

Also adds AUTHOR_MAP entry for the salvaged PR #13902 commit.

scripts/release.py

@@ -1040,6 +1040,7 @@ AUTHOR_MAP = {
     "zhang9w0v5@qq.com": "zhang9w0v5",
     "fuleinist@outlook.com": "fuleinist",
     "43494187+Llugaes@users.noreply.github.com": "Llugaes",
+    "xiangji.chen@centurygame.com": "Llugaes",
     "fengtianyu88@users.noreply.github.com": "fengtianyu88",
     "l.moncany@gmail.com": "lmoncany",
     "fatinghenji@users.noreply.github.com": "fatinghenji",