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/index.md

@@ -94,3 +94,5 @@ status: "draft"
 - [W02. ハートビートを設定する](w02-websocket-ping)
 - [W03. 接続クローズをハンドリングする](w03-websocket-close)
 - [W04. バイナリフレームを送受信する](w04-websocket-binary)
+- [W05. wss接続でTLSを設定する](w05-websocket-tls)
+- [W06. タイムアウトを設定する](w06-websocket-timeouts)