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>

frontend/src/pages/SessionDetailPage.tsx

@@ -3,17 +3,19 @@ import { useParams, useNavigate } from 'react-router-dom'
 import { Copy, Check, Eye } from 'lucide-react'
 import { sessionsApi } from '@/api'
 import { ExportPreviewModal } from '@/components/session/ExportPreviewModal'
+import { useUserPreferencesStore } from '@/store/userPreferencesStore'
 import type { Session, SessionExport } from '@/types'
 import { cn } from '@/lib/utils'
 
 export function SessionDetailPage() {
   const { id } = useParams<{ id: string }>()
   const navigate = useNavigate()
+  const { defaultExportFormat } = useUserPreferencesStore()
   const [session, setSession] = useState<Session | null>(null)
   const [isLoading, setIsLoading] = useState(true)
   const [error, setError] = useState<string | null>(null)
   const [isExporting, setIsExporting] = useState(false)
-  const [exportFormat, setExportFormat] = useState<'markdown' | 'text' | 'html'>('markdown')
+  const [exportFormat, setExportFormat] = useState<'markdown' | 'text' | 'html'>(defaultExportFormat)
   const [exportContent, setExportContent] = useState<string | null>(null)
   const [showPreview, setShowPreview] = useState(false)
   const [copied, setCopied] = useState(false)