Web: tune httpd config to reduce browser freezes on slow ESP32

The ESP32 processes HTTP requests sequentially on a single task.
Under load — generating chunked HTML pages, running commands, or
serving sequential stats API calls — it can be slow to send data
or loop back to accept the next request.  The previous 2-second
recv/send timeouts were too tight for this: the httpd layer would
drop connections mid-transfer, causing the browser to hang or
show incomplete pages.

Raise recv_wait_timeout and send_wait_timeout from 2 s to 10 s
on both the HTTPS and HTTP-redirect servers, giving the ESP32
enough headroom to finish generating and sending responses without
the transport layer tearing down the connection prematurely.

Set backlog_conn to 0 on both servers. With the previous backlog
of 2, incoming connections completed the TCP handshake and queued
in the kernel while the ESP32 was busy.  The browser saw the
connection as open but received no HTTP response, causing it to
freeze indefinitely.  With backlog 0 (lwIP minimum), connections
that cannot be immediately accepted are refused outright, giving
the browser a fast, recoverable error instead of a silent hang.

Enable lru_purge_enable on the HTTPS server.  Browsers hold
keep-alive connections open for reuse.  With max_open_sockets = 2,
both slots can be occupied by idle keep-alive connections from the
same session, blocking a new connection attempt entirely.  LRU
purge automatically closes the least-recently-used idle keep-alive
connection to make room, ensuring the single client can always
reconnect without a server restart.

src/helpers/web/WebPanelServer.cpp

@@ -2568,9 +2568,10 @@ bool WebPanelServer::start() {
   config.httpd.max_open_sockets = 2;
   config.httpd.max_uri_handlers = 7;
   config.httpd.max_resp_headers = 4;
-  config.httpd.backlog_conn = 2;
-  config.httpd.recv_wait_timeout = 2;
-  config.httpd.send_wait_timeout = 2;
+  config.httpd.backlog_conn = 0;
+  config.httpd.recv_wait_timeout = 10;
+  config.httpd.send_wait_timeout = 10;
+  config.httpd.lru_purge_enable = true;
   config.httpd.stack_size = kWebServerStackSize;
   config.httpd.task_priority = tskIDLE_PRIORITY + 2;
   config.httpd.core_id = 0;
@@ -2613,9 +2614,9 @@ bool WebPanelServer::start() {
   redirect_config.max_open_sockets = 2;
   redirect_config.max_uri_handlers = 1;
   redirect_config.max_resp_headers = 4;
-  redirect_config.backlog_conn = 2;
-  redirect_config.recv_wait_timeout = 2;
-  redirect_config.send_wait_timeout = 2;
+  redirect_config.backlog_conn = 0;
+  redirect_config.recv_wait_timeout = 10;
+  redirect_config.send_wait_timeout = 10;
   redirect_config.stack_size = kWebServerStackSize;
   redirect_config.task_priority = tskIDLE_PRIORITY + 2;
   redirect_config.core_id = 0;