Pipeline: Remove CURL as a dependency, add new HTTP module (#219)

Rationale: 

HTTP is a supporting concern in the pipeline, used only for Wikipedia enrichment calls. libcurl's C API required significant boilerplate to wrap safely. cpp-httplib is a header-only library that covers the same functionality with far less overhead and no manual resource management.

tooling/pipeline/src/web_client/http_web_client.cc

@@ -0,0 +1,61 @@
+/**
+* @file web_client/http_web_client.cc
+ * @brief cpp-httplib implementation of WebClient.
+ */
+
+#include "web_client/http_web_client.h"
+
+#include <httplib.h>
+
+#include <regex>
+#include <stdexcept>
+#include <string>
+#include <utility>
+
+namespace {
+constexpr time_t kConnectionTimeoutSeconds = 5;
+constexpr time_t kReadTimeoutSeconds = 10;
+
+constexpr int kSuccessMin = 200;
+constexpr int kSuccessMax = 300;
+const std::regex kUrlRegex(
+    R"(^(https?://[^/?#]+)(/[^?#]*(?:\?[^#]*)?(?:#.*)?)?)");
+
+std::pair<std::string, std::string> SplitUrl(const std::string& url) {
+  std::smatch match;
+  if (!std::regex_match(url, match, kUrlRegex)) {
+    throw std::invalid_argument("[HttpWebClient] Malformed URL: " + url);
+  }
+
+  return {match[1].str(), match[2].matched ? match[2].str() : "/"};
+}
+} // namespace
+
+std::string HttpWebClient::Get(const std::string& url) {
+  const auto [origin, path] = SplitUrl(url);
+
+  httplib::Client client(origin);
+  client.set_follow_location(true);
+  client.set_connection_timeout(kConnectionTimeoutSeconds);
+  client.set_read_timeout(kReadTimeoutSeconds);
+
+  const auto result = client.Get(path);
+
+  if (!result) {
+    throw std::runtime_error(
+        "[HttpWebClient] Request failed for URL: " + url +
+        " — " + httplib::to_string(result.error()));
+  }
+
+  if (result->status < kSuccessMin || result->status >= kSuccessMax) {
+    throw std::runtime_error(
+        "[HttpWebClient] HTTP " + std::to_string(result->status) +
+        " for URL: " + url);
+  }
+
+  return result->body;
+}
+
+std::string HttpWebClient::UrlEncode(const std::string& value) {
+  return httplib::encode_uri_component(value);
+}