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/helpers.cpp

@@ -147,7 +147,17 @@ std::pair<std::string, std::string> ParseTwoLineResponse(
       std::transform(low.begin(), low.end(), low.begin(), [](unsigned char c) {
          return static_cast<char>(std::tolower(c));
       });
-      if (!l.empty() && l.front() == '<' && low.back() == '>') continue;
+      // Filter known thinking tags like <think>...</think>, but be conservative
+      // to avoid removing legitimate output. Only filter specific known
+      // patterns.
+      if (!l.empty() && l.front() == '<' && low.back() == '>') {
+         // Only filter if it's a known thinking tag: <think>, <reasoning>, etc.
+         if (low.find("think") != std::string::npos ||
+             low.find("reasoning") != std::string::npos ||
+             low.find("reflect") != std::string::npos) {
+            continue;
+         }
+      }
       if (low.rfind("okay,", 0) == 0 || low.rfind("hmm", 0) == 0) continue;
       filtered.push_back(std::move(l));
    }