Complete audit history API: update endpoints, download logging, and history models (#20)

- Add PUT /api/v1/projects/{project} endpoint with audit logging
- Add PUT /api/v1/project/{project}/packages/{package} endpoint with audit logging
- Add artifact.download audit logging to download endpoint
- Enhance tag history endpoint with artifact metadata and pagination
- Add ProjectHistory and PackageHistory models for metadata change tracking
- Add database triggers for automatic history population on updates
- Add migration 004_history_tables.sql with tables and triggers

backend/app/models.py

@@ -304,3 +304,51 @@ class AuditLog(Base):
         Index("idx_audit_logs_resource_timestamp", "resource", "timestamp"),
         Index("idx_audit_logs_user_timestamp", "user_id", "timestamp"),
     )
+
+
+class ProjectHistory(Base):
+    """Track changes to project metadata over time."""
+
+    __tablename__ = "project_history"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    project_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("projects.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    field_name = Column(String(100), nullable=False)
+    old_value = Column(Text)
+    new_value = Column(Text)
+    changed_at = Column(DateTime(timezone=True), default=datetime.utcnow)
+    changed_by = Column(String(255), nullable=False)
+
+    __table_args__ = (
+        Index("idx_project_history_project_id", "project_id"),
+        Index("idx_project_history_changed_at", "changed_at"),
+        Index("idx_project_history_project_changed_at", "project_id", "changed_at"),
+    )
+
+
+class PackageHistory(Base):
+    """Track changes to package metadata over time."""
+
+    __tablename__ = "package_history"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    package_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("packages.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    field_name = Column(String(100), nullable=False)
+    old_value = Column(Text)
+    new_value = Column(Text)
+    changed_at = Column(DateTime(timezone=True), default=datetime.utcnow)
+    changed_by = Column(String(255), nullable=False)
+
+    __table_args__ = (
+        Index("idx_package_history_package_id", "package_id"),
+        Index("idx_package_history_changed_at", "changed_at"),
+        Index("idx_package_history_package_changed_at", "package_id", "changed_at"),
+    )