Documentation Site on GitHub Pages (#2376)

* Add initial documentations

* Update documentation for Basic Client and add WebSocket section

* feat: add a static site generator with multi-language support

- Introduced a new Rust-based static site generator in the `docs-gen` directory.
- Implemented core functionality for building sites from markdown files, including:
  - Configuration loading from `config.toml`.
  - Markdown rendering with frontmatter support.
  - Navigation generation based on page structure.
  - Static file copying and output directory management.
- Added templates for base layout, pages, and portal.
- Created a CSS file for styling and a JavaScript file for interactive features like language selection and theme toggling.
- Updated documentation source with new configuration and example pages in English and Japanese.
- Added a `justfile` target for building the documentation site.

* Add language/theme toggle functionality

- Created a new Japanese tour index page at docs/ja/tour/index.html
- Implemented navigation links for various sections of the cpp-httplib tutorial
- Added a language selector to switch between English and Japanese
- Introduced theme toggle functionality to switch between light and dark modes
- Added mobile sidebar toggle for better navigation on smaller screens

docs-src/pages/en/tour/06-https-client.md

@@ -0,0 +1,122 @@
+---
+title: "HTTPS Client"
+order: 6
+---
+
+In the previous chapter, you set up OpenSSL. Now let's put it to use with an HTTPS client. You can use the same `httplib::Client` from Chapter 2. Just pass a URL with the `https://` scheme to the constructor.
+
+## GET Request
+
+Let's try accessing a real HTTPS site.
+
+```cpp
+#define CPPHTTPLIB_OPENSSL_SUPPORT
+#include "httplib.h"
+#include <iostream>
+
+int main() {
+    httplib::Client cli("https://nghttp2.org");
+
+    auto res = cli.Get("/");
+    if (res) {
+        std::cout << res->status << std::endl;           // 200
+        std::cout << res->body.substr(0, 100) << std::endl;  // First 100 chars of the HTML
+    } else {
+        std::cout << "Error: " << httplib::to_string(res.error()) << std::endl;
+    }
+}
+```
+
+In Chapter 2, you wrote `httplib::Client cli("http://localhost:8080")`. All you need to change is the scheme to `https://`. Every API you learned in Chapter 2 -- `Get()`, `Post()`, and so on -- works exactly the same way.
+
+```sh
+curl https://nghttp2.org/
+```
+
+## Specifying a Port
+
+The default port for HTTPS is 443. If you need a different port, include it in the URL.
+
+```cpp
+httplib::Client cli("https://localhost:8443");
+```
+
+## CA Certificate Verification
+
+When connecting over HTTPS, `httplib::Client` verifies the server certificate by default. It only connects to servers whose certificate was issued by a trusted CA (Certificate Authority).
+
+CA certificates are loaded automatically from the Keychain on macOS, the system CA certificate store on Linux, and the Windows certificate store on Windows. In most cases, no extra configuration is needed.
+
+### Specifying a CA Certificate File
+
+On some environments, the system CA certificates may not be found. In that case, use `set_ca_cert_path()` to specify the path directly.
+
+```cpp
+httplib::Client cli("https://nghttp2.org");
+cli.set_ca_cert_path("/etc/ssl/certs/ca-certificates.crt");
+
+auto res = cli.Get("/");
+```
+
+```sh
+curl --cacert /etc/ssl/certs/ca-certificates.crt https://nghttp2.org/
+```
+
+### Disabling Certificate Verification
+
+During development, you might want to connect to a server with a self-signed certificate. You can disable verification for that.
+
+```cpp
+httplib::Client cli("https://localhost:8443");
+cli.enable_server_certificate_verification(false);
+
+auto res = cli.Get("/");
+```
+
+```sh
+curl -k https://localhost:8443/
+```
+
+Never disable this in production. It opens you up to man-in-the-middle attacks.
+
+## Following Redirects
+
+When accessing HTTPS sites, you'll often encounter redirects. For example, `http://` to `https://`, or a bare domain to `www`.
+
+By default, redirects are not followed. You can check the redirect target in the `Location` header.
+
+```cpp
+httplib::Client cli("https://nghttp2.org");
+
+auto res = cli.Get("/httpbin/redirect/3");
+if (res) {
+    std::cout << res->status << std::endl;  // 302
+    std::cout << res->get_header_value("Location") << std::endl;
+}
+```
+
+```sh
+curl https://nghttp2.org/httpbin/redirect/3
+```
+
+Call `set_follow_location(true)` to automatically follow redirects and get the final response.
+
+```cpp
+httplib::Client cli("https://nghttp2.org");
+cli.set_follow_location(true);
+
+auto res = cli.Get("/httpbin/redirect/3");
+if (res) {
+    std::cout << res->status << std::endl;  // 200 (the final response)
+}
+```
+
+```sh
+curl -L https://nghttp2.org/httpbin/redirect/3
+```
+
+## Next Steps
+
+Now you know how to use the HTTPS client. Next, let's set up your own HTTPS server. We'll start with creating a self-signed certificate.
+
+**Next:** [HTTPS Server](../07-https-server)