Fix nginx rate limit blocking accept: exact match for send request location

location /api/connections/request was a prefix match, unintentionally
rate-limiting /api/connections/requests/incoming, /outgoing, and
/requests/{id}/respond at 3r/m. This caused the accept button on toast
notifications to get 429'd when clicked immediately — the incoming
requests poll + outgoing poll had already exhausted the rate limit.

Changed to exact match (= /api/connections/request) so only the send
endpoint is rate-limited, not the entire /requests/* tree.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/nginx.conf

@@ -92,8 +92,8 @@ server {
         include /etc/nginx/proxy-params.conf;
     }
 
-    # Connection request — rate-limited to prevent spam
-    location /api/connections/request {
+    # Connection request (send) — exact match to avoid catching /requests/*
+    location = /api/connections/request {
         limit_req zone=conn_request_limit burst=3 nodelay;
         limit_req_status 429;
         include /etc/nginx/proxy-params.conf;