feat(interest): add public interest tracking for members of Congress

Adds Google Trends, NewsAPI, and Google News RSS scoring for members,
mirroring the existing bill interest pipeline. Member profiles now show
a Public Interest chart (with signal breakdown) and a Related News panel.

Key changes:
- New member_trend_scores + member_news_articles tables (migration 0008)
- fetch_gnews_articles() added to news_service for unlimited RSS article storage
- Bill news fetcher now combines NewsAPI + Google News RSS (more coverage)
- New member_interest Celery worker with scheduled news + trend tasks
- GET /members/{id}/trend and /news API endpoints
- TrendChart redesigned with signal breakdown badges and bar+line combo chart
- NewsPanel accepts generic article shape (bills and members)

Co-Authored-By: Jack Levy

backend/app/models/member.py

@@ -31,3 +31,11 @@ class Member(Base):
     updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
 
     bills = relationship("Bill", back_populates="sponsor", foreign_keys="Bill.sponsor_id")
+    trend_scores = relationship(
+        "MemberTrendScore", back_populates="member",
+        order_by="desc(MemberTrendScore.score_date)", cascade="all, delete-orphan"
+    )
+    news_articles = relationship(
+        "MemberNewsArticle", back_populates="member",
+        order_by="desc(MemberNewsArticle.published_at)", cascade="all, delete-orphan"
+    )