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/team.py

@@ -11,6 +11,7 @@ if TYPE_CHECKING:
     from app.models.tree import Tree
     from app.models.category import TreeCategory
     from app.models.tag import TreeTag
+    from app.models.step_category import StepCategory
 
 
 class Team(Base):
@@ -32,3 +33,4 @@ class Team(Base):
     trees: Mapped[list["Tree"]] = relationship("Tree", back_populates="team")
     categories: Mapped[list["TreeCategory"]] = relationship("TreeCategory", back_populates="team")
     tags: Mapped[list["TreeTag"]] = relationship("TreeTag", back_populates="team")
+    step_categories: Mapped[list["StepCategory"]] = relationship("StepCategory", back_populates="team")