feat(analytics): add flow tracking columns and psa_activity_logs table

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

backend/app/models/psa_activity_log.py

@@ -0,0 +1,28 @@
+"""PSA activity log — tracks time entries, note posts, and status updates pushed to PSA."""
+import uuid
+from datetime import datetime, timezone
+from typing import Optional
+
+from sqlalchemy import String, DateTime, ForeignKey, Float
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.dialects.postgresql import UUID
+
+from app.core.database import Base
+
+
+class PsaActivityLog(Base):
+    __tablename__ = "psa_activity_logs"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("accounts.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    session_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("ai_sessions.id", ondelete="SET NULL"), nullable=True
+    )
+    activity_type: Mapped[str] = mapped_column(String(50), nullable=False)
+    hours_logged: Mapped[Optional[float]] = mapped_column(Float, nullable=True)
+    psa_ticket_id: Mapped[Optional[str]] = mapped_column(String(100), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )