feat: personal notes on bill detail pages

- bill_notes table (migration 0014): user_id, bill_id, content, pinned,
  created_at, updated_at; unique constraint (user_id, bill_id)
- BillNote SQLAlchemy model with back-refs on User and Bill
- GET/PUT/DELETE /api/notes/{bill_id} — auth-required, one note per (user, bill)
- NotesPanel component: collapsible, auto-resize textarea, pin toggle,
  save + delete; shows last-saved date and pin indicator in collapsed header
- Pinned notes render above BriefPanel; unpinned render below DraftLetterPanel
- Guests see nothing (token guard in component + query disabled)

Co-Authored-By: Jack Levy

backend/app/models/__init__.py

@@ -4,6 +4,7 @@ from app.models.follow import Follow
 from app.models.member import Member
 from app.models.member_interest import MemberTrendScore, MemberNewsArticle
 from app.models.news import NewsArticle
+from app.models.note import BillNote
 from app.models.notification import NotificationEvent
 from app.models.setting import AppSetting
 from app.models.trend import TrendScore
@@ -15,6 +16,7 @@ __all__ = [
     "BillAction",
     "BillDocument",
     "BillBrief",
+    "BillNote",
     "Follow",
     "Member",
     "MemberTrendScore",

backend/app/models/bill.py

@@ -39,6 +39,7 @@ class Bill(Base):
     news_articles = relationship("NewsArticle", back_populates="bill", order_by="desc(NewsArticle.published_at)")
     trend_scores = relationship("TrendScore", back_populates="bill", order_by="desc(TrendScore.score_date)")
     committee_bills = relationship("CommitteeBill", back_populates="bill")
+    notes = relationship("BillNote", back_populates="bill", cascade="all, delete-orphan")
 
     __table_args__ = (
         Index("ix_bills_congress_number", "congress_number"),

backend/app/models/note.py

@@ -0,0 +1,26 @@
+from sqlalchemy import Boolean, Column, DateTime, ForeignKey, Index, Integer, String, Text, UniqueConstraint
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+class BillNote(Base):
+    __tablename__ = "bill_notes"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    bill_id = Column(String, ForeignKey("bills.bill_id", ondelete="CASCADE"), nullable=False)
+    content = Column(Text, nullable=False)
+    pinned = Column(Boolean, nullable=False, default=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
+
+    user = relationship("User", back_populates="bill_notes")
+    bill = relationship("Bill", back_populates="notes")
+
+    __table_args__ = (
+        UniqueConstraint("user_id", "bill_id", name="uq_bill_notes_user_bill"),
+        Index("ix_bill_notes_user_id", "user_id"),
+        Index("ix_bill_notes_bill_id", "bill_id"),
+    )

backend/app/models/user.py

@@ -19,3 +19,4 @@ class User(Base):
 
     follows = relationship("Follow", back_populates="user", cascade="all, delete-orphan")
     notification_events = relationship("NotificationEvent", back_populates="user", cascade="all, delete-orphan")
+    bill_notes = relationship("BillNote", back_populates="user", cascade="all, delete-orphan")