refactor(proxy): simplify verbose logging output

- Remove response JSON full output logging in response_processor
- Remove per-request INFO logs in provider_router (failover status, provider selection)
- Change model mapping log from INFO to DEBUG
- Change usage logging failure from INFO to WARN
- Remove redundant debug logs for circuit breaker operations

Reduces log noise significantly while preserving important warnings and errors.

src-tauri/src/proxy/handlers.rs

@@ -483,6 +483,6 @@ async fn log_usage(
         None, // provider_type
         is_streaming,
     ) {
-        log::warn!("记录使用量失败: {e}");
+        log::warn!("[USG-001] 记录使用量失败: {e}");
     }
 }