Add a Blogger delivery channel with one-time OAuth setup

BloggerDeliverer posts each briefing (markdown -> HTML, H1 becomes the
post title with the report headline) via the Blogger API v3 using a
long-lived refresh token; `us2kr blogger-auth` runs the loopback OAuth
flow once and prints the BLOGGER_* lines for .env. Enabled only when
all four BLOGGER_* settings are present.

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

.env.example

@@ -8,6 +8,15 @@ MINIMAX_FALLBACK_MODELS=MiniMax-M2.7,MiniMax-M2.5
 TELEGRAM_BOT_TOKEN=
 TELEGRAM_CHAT_ID=
 
+# Blogger 자동 발행 (선택) — 4개 모두 채우면 브리핑을 블로그에 게시.
+# 발급: Google Cloud에서 Blogger API 활성화 + OAuth 데스크톱 클라이언트 생성 후 `us2kr blogger-auth`
+BLOGGER_CLIENT_ID=
+BLOGGER_CLIENT_SECRET=
+BLOGGER_REFRESH_TOKEN=
+BLOGGER_BLOG_ID=
+# 게시물 라벨 CSV (기본: 미국증시,마감브리핑)
+BLOGGER_LABELS=
+
 # FRED (선택) — 경제지표 실제 발표값
 FRED_API_KEY=