fix: address critical correctness, reliability, and design issues in pipeline

CORRECTNESS FIXES:
- json_loader: Add RollbackTransaction() and call it on exception instead of
  CommitTransaction(). Prevents partial data corruption on parse/disk errors.
- wikipedia_service: Fix invalid MediaWiki API parameter explaintext=true ->
  explaintext=1. Now returns plain text instead of HTML markup in contexts.
- helpers: Fix ParseTwoLineResponse filter to only remove known thinking tags
  (<think>, <reasoning>, <reflect>) instead of any <...> pattern. Prevents
  silently removing legitimate output like <username>content</username>.

RELIABILITY & DESIGN IMPROVEMENTS:
- load/main: Make n_ctx (context window size) configurable via --n-ctx flag
  (default 2048, range 1-32768) to support larger models like Qwen3-14B.
- generate_brewery: Prevent retry prompt growth by extracting location context
  into constant and using compact retry format (error + schema + location only).
  Avoids token truncation on final retry attempts.
- database: Fix data representativeness by changing QueryCities from
  ORDER BY name (alphabetic bias) to ORDER BY RANDOM() for unbiased sampling.
  Convert all SQLITE_STATIC to SQLITE_TRANSIENT to prevent use-after-free risks.

POLISH:
- infer: Advance sampling seed between generation calls to improve diversity
  across brewery and user generation.
- data_downloader: Remove unnecessary commit hash truncation; use full hash.
- json_loader: Fix misleading log message from "RapidJSON" to "Boost.JSON".

pipeline/src/json_handling/json_loader.cpp

@@ -11,7 +11,7 @@ void JsonLoader::LoadWorldCities(const std::string& json_path,
    constexpr size_t kBatchSize = 10000;
 
    auto startTime = std::chrono::high_resolution_clock::now();
-   spdlog::info("\nLoading {} (streaming RapidJSON SAX)...", json_path);
+   spdlog::info("\nLoading {} (streaming Boost.JSON SAX)...", json_path);
 
    db.BeginTransaction();
    bool transactionOpen = true;
@@ -44,7 +44,8 @@ void JsonLoader::LoadWorldCities(const std::string& json_path,
       }
    } catch (...) {
       if (transactionOpen) {
-         db.CommitTransaction();
+         db.RollbackTransaction();
+         transactionOpen = false;
       }
       throw;
    }