feat: add onboarding, branding, and supporting data models, migrations, and schemas

Add onboarding_dismissed and branding columns (logo_data, logo_content_type,
company_display_name) to users and teams models. Create SessionSupportingData
model for attaching text snippets and screenshots to sessions. Add Pydantic
schemas for onboarding status, branding responses, and supporting data CRUD.
Update SessionExport to accept pdf format.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/models/supporting_data.py

@@ -0,0 +1,25 @@
+import uuid
+from datetime import datetime, timezone
+from typing import Optional
+
+from sqlalchemy import DateTime, Enum, ForeignKey, Integer, String, Text
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.core.database import Base
+
+
+class SessionSupportingData(Base):
+    __tablename__ = "session_supporting_data"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    session_id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), ForeignKey("sessions.id", ondelete="CASCADE"), nullable=False, index=True)
+    label: Mapped[str] = mapped_column(String(255), nullable=False)
+    data_type: Mapped[str] = mapped_column(Enum("text_snippet", "screenshot", name="supporting_data_type"), nullable=False)
+    content: Mapped[str] = mapped_column(Text, nullable=False)
+    content_type: Mapped[Optional[str]] = mapped_column(String(50), nullable=True)
+    sort_order: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc), nullable=False)
+    updated_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc), nullable=False)
+
+    session = relationship("Session", back_populates="supporting_data")