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/reading-plans/route.ts

@@ -0,0 +1,48 @@
+import { NextResponse } from 'next/server'
+import { prisma } from '@/lib/db'
+
+export const runtime = 'nodejs'
+
+/**
+ * GET /api/reading-plans
+ * Get all available predefined reading plans
+ */
+export async function GET(request: Request) {
+  try {
+    const url = new URL(request.url)
+    const language = url.searchParams.get('language') || 'en'
+
+    const plans = await prisma.readingPlan.findMany({
+      where: {
+        isActive: true,
+        type: 'PREDEFINED',
+        language: language
+      },
+      select: {
+        id: true,
+        name: true,
+        description: true,
+        duration: true,
+        difficulty: true,
+        language: true,
+        type: true,
+        createdAt: true
+      },
+      orderBy: {
+        duration: 'asc'
+      }
+    })
+
+    return NextResponse.json({
+      success: true,
+      plans
+    })
+
+  } catch (error) {
+    console.error('Reading plans fetch error:', error)
+    return NextResponse.json(
+      { error: 'Failed to fetch reading plans' },
+      { status: 500 }
+    )
+  }
+}