feat: track upstream request ID and prevent response header override

When proxying through another new-api instance, the upstream
X-Oneapi-Request-Id was overwriting the local one in client responses.
This adds a new `upstream_request_id` field to the logs table, captures
the upstream ID during relay, and filters it from being copied back to
the client. Frontend gains search/filter and detail display support.

web/default/src/routes/_authenticated/usage-logs/$section.tsx

@@ -37,6 +37,7 @@ const usageLogsSearchSchema = z.object({
   group: z.string().optional().catch(''),
   username: z.string().optional().catch(''),
   requestId: z.string().optional().catch(''),
+  upstreamRequestId: z.string().optional().catch(''),
   startTime: z.number().optional(),
   endTime: z.number().optional(),
 })