Add WebSocket TLS and timeout recipes to the Cookbook

T04 (mTLS) had grown a "WebSocketClient" subsection describing
wss:// client certificates, and c12/t02 were getting similar
WebSocketClient asides for timeouts and CA paths. The Cookbook's
own index already separates WebSocket into its own category
(W01-W04) from TLS/Security (T01-T05) and Client (C01-C19), so
burying WebSocketClient specifics inside those pages fought the
site's structure.

Move that content into two new recipes under the WebSocket
category instead:

- W05: wss:// TLS setup (set_ca_cert_path CA directory parity,
  PemMemory client certificate)
- W06: WebSocketClient's three timeouts, including the recently
  added chrono overloads

T04, T02, C12, and W01 now carry a single reference link to the
new pages instead of duplicated explanations, matching the site's
existing cross-link convention.

While rewriting T04's client-side section, noticed it documented
SSLClient's file-path constructor but not its PemMemory one, even
though the server-side section covered both forms for SSLServer.
Added the missing PemMemory example so both sides are symmetric.

docs-src/pages/en/cookbook/c12-timeouts.md

@@ -48,3 +48,5 @@ cli.set_read_timeout(10s);
 ```
 
 > **Warning:** The read timeout covers a single receive call — not the whole request. If data keeps trickling in during a large download, the request can take half an hour without ever hitting the timeout. To cap the total request time, use [C13. Set an overall timeout](../c13-max-timeout).
+
+> For WebSocket client timeouts, see [W06. Set Timeouts](../w06-websocket-timeouts).