Add step library foundation and user preferences (Issues #3, #5, #6, #7)

Issue #3: User Preferences - export format default
- Add userPreferencesStore with localStorage persistence
- Create Settings page with export format dropdown and theme toggle
- SessionDetailPage now uses default export format from preferences

Issue #5: Step Categories - database table and seed data
- Migration 007: step_categories table with team scoping
- Seed 10 default global categories (Citrix/VDI, AD, M365, etc.)
- Full CRUD API at /api/v1/step-categories

Issue #6: Step Library - database schema
- Migration 008: step_library, step_ratings, step_usage_log tables
- Support for decision/action/solution step types
- Visibility levels: private, team, public
- Rating aggregates and usage tracking

Issue #7: Step Library - CRUD API endpoints
- Full CRUD at /api/v1/steps with visibility filtering
- Full-text search endpoint
- Popular tags endpoint
- Rating/review system with verified use tracking

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/models/step_category.py

@@ -0,0 +1,64 @@
+import uuid
+from datetime import datetime, timezone
+from typing import Optional, TYPE_CHECKING
+from sqlalchemy import String, Text, DateTime, ForeignKey, Boolean, Integer, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy.dialects.postgresql import UUID
+from app.core.database import Base
+
+if TYPE_CHECKING:
+    from app.models.team import Team
+    from app.models.user import User
+
+
+class StepCategory(Base):
+    """Admin-managed categories for organizing step library entries.
+
+    Categories can be:
+    - Global (team_id=NULL): Created by Patherly admins, visible to all
+    - Team-specific (team_id set): Created by team admins, visible to team members
+    """
+    __tablename__ = "step_categories"
+    __table_args__ = (
+        UniqueConstraint('slug', 'team_id', name='uq_step_categories_slug_team'),
+    )
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        primary_key=True,
+        default=uuid.uuid4
+    )
+    name: Mapped[str] = mapped_column(String(100), nullable=False)
+    slug: Mapped[str] = mapped_column(String(100), nullable=False, index=True)
+    description: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
+    team_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("teams.id", ondelete="CASCADE"),
+        nullable=True,
+        index=True
+    )
+    display_order: Mapped[int] = mapped_column(Integer, nullable=False, default=0, index=True)
+    is_active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
+    created_by: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("users.id", ondelete="SET NULL"),
+        nullable=True
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(timezone.utc)
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(timezone.utc),
+        onupdate=lambda: datetime.now(timezone.utc)
+    )
+
+    # Relationships
+    team: Mapped[Optional["Team"]] = relationship("Team", back_populates="step_categories")
+    creator: Mapped[Optional["User"]] = relationship("User", foreign_keys=[created_by])
+
+    @property
+    def is_global(self) -> bool:
+        """Returns True if this is a global category (not team-specific)."""
+        return self.team_id is None