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/includes/data_generation/llama_generator.h

@@ -16,6 +16,8 @@ class LlamaGenerator final : public DataGenerator {
 
    void SetSamplingOptions(float temperature, float top_p, int seed = -1);
 
+   void SetContextSize(uint32_t n_ctx);
+
    void Load(const std::string& model_path) override;
    BreweryResult GenerateBrewery(const std::string& city_name,
                                  const std::string& country_name,
@@ -39,6 +41,7 @@ class LlamaGenerator final : public DataGenerator {
    float sampling_temperature_ = 0.8f;
    float sampling_top_p_ = 0.92f;
    uint32_t sampling_seed_ = 0xFFFFFFFFu;
+   uint32_t n_ctx_ = 2048;
 };
 
 #endif  // BIERGARTEN_PIPELINE_DATA_GENERATION_LLAMA_GENERATOR_H_