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/wikipedia/wikipedia_service.cpp

@@ -11,7 +11,7 @@ std::string WikipediaService::FetchExtract(std::string_view query) {
    const std::string encoded = client_->UrlEncode(std::string(query));
    const std::string url =
        "https://en.wikipedia.org/w/api.php?action=query&titles=" + encoded +
-       "&prop=extracts&explaintext=true&format=json";
+       "&prop=extracts&explaintext=1&format=json";
 
    const std::string body = client_->Get(url);
 
@@ -19,16 +19,27 @@ std::string WikipediaService::FetchExtract(std::string_view query) {
    boost::json::value doc = boost::json::parse(body, ec);
 
    if (!ec && doc.is_object()) {
-      auto& pages = doc.at("query").at("pages").get_object();
-      if (!pages.empty()) {
-         auto& page = pages.begin()->value().get_object();
-         if (page.contains("extract") && page.at("extract").is_string()) {
-            std::string extract(page.at("extract").as_string().c_str());
-            spdlog::debug("WikipediaService fetched {} chars for '{}'",
-                          extract.size(), query);
-            return extract;
+      try {
+         auto& pages = doc.at("query").at("pages").get_object();
+         if (!pages.empty()) {
+            auto& page = pages.begin()->value().get_object();
+            if (page.contains("extract") && page.at("extract").is_string()) {
+               std::string extract(page.at("extract").as_string().c_str());
+               spdlog::debug("WikipediaService fetched {} chars for '{}'",
+                             extract.size(), query);
+               return extract;
+            }
          }
+      } catch (const std::exception& e) {
+         spdlog::warn(
+             "WikipediaService: failed to parse response structure for '{}': "
+             "{}",
+             query, e.what());
+         return {};
       }
+   } else if (ec) {
+      spdlog::warn("WikipediaService: JSON parse error for '{}': {}", query,
+                   ec.message());
    }
 
    return {};