chore(quality): retighten the chat.ts unused-vars suppression to 8

#12975 lowered this to 8 when it started using runtimeOptions.correlationId,
but a later merge today carried the old 9 back in. The file has 8 violations,
so the entry rejects any commit that stages it.

changelog.d/maintenance/chat-unused-vars-count-20260911.md

@@ -0,0 +1 @@
+- **chore(quality):** retighten the `src/sse/handlers/chat.ts` unused-vars suppression count to the 8 violations that actually remain

config/quality/eslint-suppressions.json

@@ -2080,7 +2080,7 @@
   },
   "src/sse/handlers/chat.ts": {
     "@typescript-eslint/no-unused-vars": {
-      "count": 9
+      "count": 8
     }
   },
   "src/sse/handlers/chatHelpers.ts": {