Pipeline: add CURL/WebClient & Wikipedia service

Introduce a pluggable web client interface and concrete CURL implementation: adds IWebClient, CURLWebClient, and CurlGlobalState (headers + curl_web_client.cpp). DataDownloader now accepts an IWebClient and delegates downloads. Add WikipediaService for cached Wikipedia summary lookups. Refactor SqliteDatabase to return full City records and update consumers accordingly. Improve JsonLoader to use batched transactions during streaming parses. Enhance LlamaGenerator with sampling options, increased token limits, JSON extraction/validation, and other parsing helpers. Modernize CMake: set policy/version, add project_options, simplify FetchContent usage (spdlog), require Boost components (program_options/json), list pipeline sources explicitly, and tweak post-build/memcheck targets. Update README to match implementation changes and new CLI/config conventions.

pipeline/includes/database.h

@@ -27,6 +27,15 @@ struct State {
   int countryId;
 };
 
+struct City {
+  /// @brief City identifier from the source dataset.
+  int id;
+  /// @brief City display name.
+  std::string name;
+  /// @brief Parent country identifier.
+  int countryId;
+};
+
 /// @brief Thread-safe SQLite wrapper for pipeline writes and readbacks.
 class SqliteDatabase {
 private:
@@ -60,8 +69,8 @@ public:
   void InsertCity(int id, int stateId, int countryId, const std::string &name,
                   double latitude, double longitude);
 
-  /// @brief Returns city id and city name pairs.
-  std::vector<std::pair<int, std::string>> QueryCities();
+  /// @brief Returns city records including parent country id.
+  std::vector<City> QueryCities();
 
   /// @brief Returns countries with optional row limit.
   std::vector<Country> QueryCountries(int limit = 0);