feat: add user settings save and reading plans with progress tracking

User Settings:
- Add /api/user/settings endpoint for persisting theme and fontSize preferences
- Update settings page with working save functionality
- Add validation and localized error messages

Reading Plans:
- Add database schema with ReadingPlan, UserReadingPlan, and UserReadingProgress models
- Create CRUD API endpoints for reading plans and progress tracking
- Build UI for browsing available plans and managing user enrollments
- Implement progress tracking with daily reading schedule
- Add streak calculation and statistics display
- Create seed data with 5 predefined plans (Bible in 1 year, 90 days, NT 30 days, Psalms 30, Gospels 30)
- Add navigation link with internationalization support

Technical:
- Update to MUI v7 Grid API (using size prop instead of xs/sm/md and removing item prop)
- Fix Next.js 15 dynamic route params (await params pattern)
- Add translations for readingPlans in all languages (en, ro, es, it)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/api/user/settings/route.ts

@@ -0,0 +1,103 @@
+import { NextResponse } from 'next/server'
+import { getUserFromToken } from '@/lib/auth'
+import { prisma } from '@/lib/db'
+
+export const runtime = 'nodejs'
+
+function getErrorMessages(locale: string = 'ro') {
+  const messages = {
+    ro: {
+      unauthorized: 'Nu esti autentificat',
+      updateFailed: 'Actualizarea setărilor a eșuat',
+      success: 'Setări actualizate cu succes',
+      invalidData: 'Date invalide'
+    },
+    en: {
+      unauthorized: 'Unauthorized',
+      updateFailed: 'Settings update failed',
+      success: 'Settings updated successfully',
+      invalidData: 'Invalid data'
+    }
+  }
+  return messages[locale as keyof typeof messages] || messages.ro
+}
+
+export async function PUT(request: Request) {
+  try {
+    const url = new URL(request.url)
+    const locale = url.searchParams.get('locale') || 'ro'
+    const messages = getErrorMessages(locale)
+
+    // Get token from authorization header
+    const authHeader = request.headers.get('authorization')
+    const token = authHeader?.replace('Bearer ', '')
+
+    if (!token) {
+      return NextResponse.json({ error: messages.unauthorized }, { status: 401 })
+    }
+
+    // Verify token and get user
+    const user = await getUserFromToken(token)
+
+    if (!user) {
+      return NextResponse.json({ error: messages.unauthorized }, { status: 401 })
+    }
+
+    // Parse request body
+    const body = await request.json()
+    const { theme, fontSize, notifications, emailUpdates, language } = body
+
+    // Validate input - allow partial updates
+    const updateData: any = {}
+
+    if (theme !== undefined) {
+      if (!['light', 'dark', 'auto'].includes(theme)) {
+        return NextResponse.json({ error: messages.invalidData }, { status: 400 })
+      }
+      updateData.theme = theme
+    }
+
+    if (fontSize !== undefined) {
+      if (!['small', 'medium', 'large'].includes(fontSize)) {
+        return NextResponse.json({ error: messages.invalidData }, { status: 400 })
+      }
+      updateData.fontSize = fontSize
+    }
+
+    // Note: notifications and emailUpdates would need additional columns in User model
+    // For now, we'll skip them or store in a JSON field if needed
+
+    // Update user settings
+    const updatedUser = await prisma.user.update({
+      where: { id: user.id },
+      data: updateData,
+      select: {
+        id: true,
+        email: true,
+        name: true,
+        role: true,
+        theme: true,
+        fontSize: true,
+        subscriptionTier: true,
+        subscriptionStatus: true,
+        conversationLimit: true,
+        conversationCount: true,
+        limitResetDate: true
+      }
+    })
+
+    return NextResponse.json({
+      success: true,
+      message: messages.success,
+      user: updatedUser
+    })
+
+  } catch (error) {
+    console.error('Settings update error:', error)
+    const url = new URL(request.url)
+    const locale = url.searchParams.get('locale') || 'ro'
+    const messages = getErrorMessages(locale)
+
+    return NextResponse.json({ error: messages.updateFailed }, { status: 500 })
+  }
+}