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/ja/cookbook/c12-timeouts.md

@@ -48,3 +48,5 @@ cli.set_read_timeout(10s);
 ```
 
 > **Warning:** 読み取りタイムアウトは「1回の受信待ち」に対するタイムアウトです。大きなファイルのダウンロードで途中ずっとデータが流れている限り、リクエスト全体で30分かかっても発火しません。リクエスト全体の時間制限を設けたい場合は[C13. 全体タイムアウトを設定する](../c13-max-timeout)を使ってください。
+
+> WebSocketクライアントのタイムアウト設定は[W06. タイムアウトを設定する](../w06-websocket-timeouts)を参照してください。