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>

us2kr/deliver/__init__.py

@@ -1,4 +1,4 @@
-"""Delivery channels: local file archive (always) + Telegram (when configured)."""
+"""Delivery channels: local file archive (always) + Telegram / Blogger (when configured)."""
 
 from __future__ import annotations
 
@@ -6,19 +6,37 @@ import logging
 
 from us2kr.config import Settings
 from us2kr.deliver.base import Deliverer, DeliveryError
+from us2kr.deliver.blogger import BloggerDeliverer
 from us2kr.deliver.file import FileDeliverer
 from us2kr.deliver.telegram import TelegramDeliverer
 
 log = logging.getLogger(__name__)
 
-__all__ = ["Deliverer", "DeliveryError", "FileDeliverer", "TelegramDeliverer", "build_deliverers"]
+__all__ = [
+    "BloggerDeliverer",
+    "Deliverer",
+    "DeliveryError",
+    "FileDeliverer",
+    "TelegramDeliverer",
+    "build_deliverers",
+]
 
 
 def build_deliverers(settings: Settings) -> list[Deliverer]:
-    """FileDeliverer always; TelegramDeliverer when both token and chat id are configured."""
+    """FileDeliverer always; Telegram / Blogger when fully configured."""
     deliverers: list[Deliverer] = [FileDeliverer(settings.reports_dir)]
     if settings.telegram_enabled:
         assert settings.telegram_bot_token and settings.telegram_chat_id  # guaranteed by telegram_enabled
         deliverers.append(TelegramDeliverer(settings.telegram_bot_token, settings.telegram_chat_id))
+    if settings.blogger_enabled:
+        deliverers.append(
+            BloggerDeliverer(
+                settings.blogger_client_id or "",
+                settings.blogger_client_secret or "",
+                settings.blogger_refresh_token or "",
+                settings.blogger_blog_id or "",
+                labels=settings.blogger_labels,
+            )
+        )
     log.info("deliverers: %s", ", ".join(d.name for d in deliverers))
     return deliverers