Add step library foundation and user preferences (#24)

## Summary
Implements Phase 2.5 Step Library Foundation:

### Issues Completed
- #3 User Preferences - export format default setting
- #5 Step Categories - database table and seed data  
- #6 Step Library - database schema and migrations
- #7 Step Library - CRUD API endpoints
- #8 Step Library - rating and review system

### Changes
**Backend:**
- Migration 007: step_categories table with 10 seeded global categories
- Migration 008: step_library, step_ratings, step_usage_log tables
- Full CRUD API for step categories (/api/v1/step-categories)
- Full CRUD API for step library (/api/v1/steps) with search, filters, ratings
- CORS support for Railway PR environments (ALLOW_RAILWAY_ORIGINS)

**Frontend:**
- User preferences store (Zustand + localStorage)
- Settings page at /settings with export format dropdown
- Default export format applied in SessionDetailPage

### Testing
- Tested in Railway PR environment
- Database seeded with 7 MSP troubleshooting trees
- All API endpoints verified working

frontend/src/components/layout/AppLayout.tsx

@@ -16,6 +16,7 @@ export function AppLayout() {
   const navItems = [
     { path: '/trees', label: 'Trees' },
     { path: '/sessions', label: 'Sessions' },
+    { path: '/settings', label: 'Settings' },
   ]
 
   return (

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)

frontend/src/pages/SettingsPage.tsx

@@ -0,0 +1,93 @@
+import { Settings } from 'lucide-react'
+import { useUserPreferencesStore } from '@/store/userPreferencesStore'
+import { useThemeStore } from '@/store/themeStore'
+import { cn } from '@/lib/utils'
+import { ThemeToggle } from '@/components/common/ThemeToggle'
+
+export function SettingsPage() {
+  const { defaultExportFormat, setDefaultExportFormat } = useUserPreferencesStore()
+  const { theme } = useThemeStore()
+
+  return (
+    <div className="container mx-auto px-4 py-8">
+      <div className="mb-8">
+        <div className="flex items-center gap-3">
+          <Settings className="h-8 w-8 text-primary" />
+          <h1 className="text-3xl font-bold text-foreground">Settings</h1>
+        </div>
+        <p className="mt-2 text-muted-foreground">
+          Manage your application preferences
+        </p>
+      </div>
+
+      <div className="max-w-2xl space-y-6">
+        {/* Appearance Section */}
+        <div className="rounded-lg border border-border bg-card p-6 shadow-sm">
+          <h2 className="text-lg font-semibold text-card-foreground">Appearance</h2>
+          <p className="mt-1 text-sm text-muted-foreground">
+            Customize how Patherly looks on your device
+          </p>
+
+          <div className="mt-4">
+            <label className="block text-sm font-medium text-card-foreground">
+              Theme
+            </label>
+            <p className="text-sm text-muted-foreground">
+              Current: {theme.charAt(0).toUpperCase() + theme.slice(1)}
+            </p>
+            <div className="mt-2">
+              <ThemeToggle />
+            </div>
+          </div>
+        </div>
+
+        {/* Export Preferences Section */}
+        <div className="rounded-lg border border-border bg-card p-6 shadow-sm">
+          <h2 className="text-lg font-semibold text-card-foreground">Export Preferences</h2>
+          <p className="mt-1 text-sm text-muted-foreground">
+            Configure default settings for session exports
+          </p>
+
+          <div className="mt-4">
+            <label
+              htmlFor="export-format"
+              className="block text-sm font-medium text-card-foreground"
+            >
+              Default Export Format
+            </label>
+            <p className="text-sm text-muted-foreground">
+              This format will be pre-selected when exporting sessions
+            </p>
+            <select
+              id="export-format"
+              value={defaultExportFormat}
+              onChange={(e) => setDefaultExportFormat(e.target.value as 'markdown' | 'text' | 'html')}
+              className={cn(
+                'mt-2 block w-full rounded-md border border-input bg-background px-3 py-2',
+                'text-sm text-foreground',
+                'focus:border-primary focus:outline-none focus:ring-1 focus:ring-primary'
+              )}
+            >
+              <option value="markdown">Markdown (.md)</option>
+              <option value="text">Plain Text (.txt)</option>
+              <option value="html">HTML (.html)</option>
+            </select>
+          </div>
+        </div>
+
+        {/* About Section */}
+        <div className="rounded-lg border border-border bg-card p-6 shadow-sm">
+          <h2 className="text-lg font-semibold text-card-foreground">About</h2>
+          <p className="mt-1 text-sm text-muted-foreground">
+            Patherly - Troubleshooting Decision Trees
+          </p>
+          <p className="mt-2 text-sm text-muted-foreground">
+            "Take the path MOST traveled."
+          </p>
+        </div>
+      </div>
+    </div>
+  )
+}
+
+export default SettingsPage

frontend/src/pages/index.ts

@@ -5,3 +5,4 @@ export { default as TreeNavigationPage } from './TreeNavigationPage'
 export { default as TreeEditorPage } from './TreeEditorPage'
 export { default as SessionHistoryPage } from './SessionHistoryPage'
 export { default as SessionDetailPage } from './SessionDetailPage'
+export { default as SettingsPage } from './SettingsPage'

frontend/src/router.tsx

@@ -9,6 +9,7 @@ import {
   TreeEditorPage,
   SessionHistoryPage,
   SessionDetailPage,
+  SettingsPage,
 } from '@/pages'
 
 export const router = createBrowserRouter([
@@ -59,6 +60,10 @@ export const router = createBrowserRouter([
         path: 'sessions/:id',
         element: <SessionDetailPage />,
       },
+      {
+        path: 'settings',
+        element: <SettingsPage />,
+      },
     ],
   },
 ])

frontend/src/store/userPreferencesStore.ts

@@ -0,0 +1,23 @@
+import { create } from 'zustand'
+import { persist } from 'zustand/middleware'
+
+type ExportFormat = 'markdown' | 'text' | 'html'
+
+interface UserPreferencesState {
+  defaultExportFormat: ExportFormat
+  setDefaultExportFormat: (format: ExportFormat) => void
+}
+
+export const useUserPreferencesStore = create<UserPreferencesState>()(
+  persist(
+    (set) => ({
+      defaultExportFormat: 'markdown',
+      setDefaultExportFormat: (format) => set({ defaultExportFormat: format }),
+    }),
+    {
+      name: 'user-preferences-storage',
+    }
+  )
+)
+
+export default useUserPreferencesStore