feat(backend): add Match + ActivityEvent ORM models

backend/src/cyclone/db.py

@@ -177,8 +177,6 @@ class Batch(Base):
         # alone (no migration runner) get the same index direction as prod.
         Index("ix_batches_parsed_at", text("parsed_at DESC")),
     )
-    # TODO(T6): when ActivityEvent model is added, mirror this pattern for
-    # `ix_activity_events_ts` on activity_events(ts DESC) per 0001_initial.sql:86.
 
 
 class Claim(Base):
@@ -283,3 +281,46 @@ class CasAdjustment(Base):
     __table_args__ = (
         Index("ix_cas_adjustments_remittance_id", "remittance_id"),
     )
+
+
+class Match(Base):
+    __tablename__ = "matches"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    claim_id: Mapped[str] = mapped_column(
+        String(64), ForeignKey("claims.id", ondelete="CASCADE"),
+        nullable=False, unique=True,
+    )
+    remittance_id: Mapped[str] = mapped_column(
+        String(64), ForeignKey("remittances.id", ondelete="CASCADE"), nullable=False
+    )
+    strategy: Mapped[str] = mapped_column(String(16), nullable=False)
+    matched_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+    prior_claim_state: Mapped[Optional[ClaimState]] = mapped_column(
+        Enum(ClaimState, native_enum=False), nullable=True
+    )
+    is_reversal: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
+
+    __table_args__ = (
+        Index("ix_matches_remittance_id", "remittance_id"),
+        Index("ix_matches_matched_at", "matched_at"),
+    )
+
+
+class ActivityEvent(Base):
+    __tablename__ = "activity_events"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    ts: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+    kind: Mapped[str] = mapped_column(String(32), nullable=False)
+    batch_id: Mapped[Optional[str]] = mapped_column(String(32), nullable=True)
+    claim_id: Mapped[Optional[str]] = mapped_column(String(64), nullable=True)
+    remittance_id: Mapped[Optional[str]] = mapped_column(String(64), nullable=True)
+    payload_json: Mapped[Optional[dict]] = mapped_column(JSONText, nullable=True)
+
+    __table_args__ = (
+        # Migration declares this as DESC; mirror the qualifier so create_all
+        # on a fresh DB (without migrations) produces identical DDL.
+        Index("ix_activity_events_ts", text("ts DESC")),
+        Index("ix_activity_events_kind", "kind"),
+    )