Add a Monday-morning weekly recap briefing

No US session closes into Monday KST, so Mondays (default 07:00, cron
in the daemon with restart catch-up) now publish a weekly review built
entirely from stored data: the quotes table collapsed into week-over-
week changes and the week's daily briefing headlines as the narrative.
The recap is a BriefingResult kind="weekly" reusing MarketPayload, so
the store, verification pass, all delivery channels (Blogger title
"미국 주간 리뷰 <monday>") and the dashboard (주간 리뷰 badge) work
unchanged. Manual runs via `run-once --weekly [--date <monday>]`.

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

us2kr/models.py

@@ -118,3 +118,6 @@ class BriefingResult(BaseModel):
     degraded: bool = False  # True when LLM failed and only the numeric table was produced
     error: str | None = None
     verification: Verification | None = None  # None: not run (disabled / degraded / verifier failed)
+    # "briefing": daily post-close briefing. "weekly": Monday-morning recap, where payload.quotes carry
+    # week-over-week changes, payload.session_date is the week's last US session and krx_date the Monday.
+    kind: Literal["briefing", "weekly"] = "briefing"