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/data_generation/llama/set_sampling_options.cpp

@@ -48,3 +48,18 @@ void LlamaGenerator::SetSamplingOptions(float temperature, float top_p,
    sampling_seed_ = (seed < 0) ? static_cast<uint32_t>(LLAMA_DEFAULT_SEED)
                                : static_cast<uint32_t>(seed);
 }
+
+void LlamaGenerator::SetContextSize(uint32_t n_ctx) {
+   /**
+    * Validate context size: must be positive and reasonable for the model
+    */
+   if (n_ctx == 0 || n_ctx > 32768) {
+      throw std::runtime_error(
+          "LlamaGenerator: context size must be in range [1, 32768]");
+   }
+
+   /**
+    * Store context size for use during model loading
+    */
+   n_ctx_ = n_ctx;
+}