feat: roll-call votes + granular alert filter fix (v0.9.5)

Roll-call votes:
- Migration 0017: bill_votes + member_vote_positions tables
- Fetch vote XML directly from House Clerk / Senate LIS URLs
  embedded in bill actions recordedVotes objects
- GET /api/bills/{id}/votes triggers background fetch on first view
- VotePanel on bill detail: yea/nay bar, result badge, followed
  member positions with Sen./Rep. title, party badge, and state

Alert filter fix:
- _should_dispatch returns True when alert_filters is None so users
  who haven't saved filters still receive all notifications

Authored-By: Jack Levy

backend/app/models/vote.py

@@ -0,0 +1,53 @@
+from sqlalchemy import Column, Date, DateTime, ForeignKey, Index, Integer, String, Text, UniqueConstraint
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+class BillVote(Base):
+    __tablename__ = "bill_votes"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    bill_id = Column(String, ForeignKey("bills.bill_id", ondelete="CASCADE"), nullable=False)
+    congress = Column(Integer, nullable=False)
+    chamber = Column(String(50), nullable=False)
+    session = Column(Integer, nullable=False)
+    roll_number = Column(Integer, nullable=False)
+    question = Column(Text)
+    description = Column(Text)
+    vote_date = Column(Date)
+    yeas = Column(Integer)
+    nays = Column(Integer)
+    not_voting = Column(Integer)
+    result = Column(String(200))
+    source_url = Column(String)
+    fetched_at = Column(DateTime(timezone=True))
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    positions = relationship("MemberVotePosition", back_populates="vote", cascade="all, delete-orphan")
+
+    __table_args__ = (
+        Index("ix_bill_votes_bill_id", "bill_id"),
+        UniqueConstraint("congress", "chamber", "session", "roll_number", name="uq_bill_votes_roll"),
+    )
+
+
+class MemberVotePosition(Base):
+    __tablename__ = "member_vote_positions"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    vote_id = Column(Integer, ForeignKey("bill_votes.id", ondelete="CASCADE"), nullable=False)
+    bioguide_id = Column(String, ForeignKey("members.bioguide_id", ondelete="SET NULL"), nullable=True)
+    member_name = Column(String(200))
+    party = Column(String(50))
+    state = Column(String(10))
+    position = Column(String(50), nullable=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    vote = relationship("BillVote", back_populates="positions")
+
+    __table_args__ = (
+        Index("ix_member_vote_positions_vote_id", "vote_id"),
+        Index("ix_member_vote_positions_bioguide_id", "bioguide_id"),
+    )