Fix usage logging dedupe and reduce stats churn

- batch console log buffer events and support batched SSE log messages
- debounce usage stats update/pending events to reduce UI/runtime churn
- avoid awaiting request-success bookkeeping before returning provider responses
- deduplicate identical usage writes in usageHistory/daily aggregates
- reduce default logger verbosity from DEBUG to INFO (overridable via LOG_LEVEL)

Co-authored-by: Cursor <cursoragent@cursor.com>

src/sse/utils/logger.js

@@ -7,7 +7,7 @@ const LOG_LEVELS = {
   ERROR: 3
 };
 
-const LEVEL = LOG_LEVELS.DEBUG;
+const LEVEL = LOG_LEVELS[process.env.LOG_LEVEL?.toUpperCase?.()] ?? LOG_LEVELS.INFO;
 
 function formatTime() {
   return new Date().toLocaleTimeString("en-US", { hour12: false });
@@ -72,4 +72,3 @@ export function maskKey(key) {
   if (!key || key.length < 8) return "***";
   return `${key.slice(0, 4)}...${key.slice(-4)}`;
 }
-