Add SearXNG news collector merged into the briefing pipeline

Optional meta-search source (SEARXNG_BASE_URL): per-query isolation,
time_range=day, merged and deduplicated with the RSS feeds. Briefings
still publish on RSS alone if the instance is down.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.env.example

@@ -11,6 +11,11 @@ TELEGRAM_CHAT_ID=
 # FRED (선택) — 경제지표 실제 발표값
 FRED_API_KEY=
 
+# SearXNG (선택) — 설정하면 RSS 외에 메타검색 뉴스도 수집 (인스턴스에 json 포맷 활성화 필요)
+SEARXNG_BASE_URL=
+# 검색어 CSV. 비우면 기본값(us2kr/collectors/searx.py DEFAULT_QUERIES)
+US2KR_SEARXNG_QUERIES=
+
 # 실행 정책
 US2KR_RUN_OFFSET_MINUTES=75
 US2KR_CATCHUP_WINDOW_HOURS=3