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>

prisma/schema.prisma

@@ -40,6 +40,8 @@ model User {
   userPrayers     UserPrayer[]
   readingHistory  ReadingHistory[]
   preferences     UserPreference[]
+  userReadingPlans UserReadingPlan[]
+  readingProgress  UserReadingProgress[]
   createdPages    Page[] @relation("PageCreator")
   updatedPages    Page[] @relation("PageUpdater")
   uploadedFiles   MediaFile[]
@@ -500,3 +502,87 @@ enum SubscriptionStatus {
   INCOMPLETE_EXPIRED
   UNPAID
 }
+
+// Reading Plans
+model ReadingPlan {
+  id          String   @id @default(uuid())
+  name        String   // "Bible in One Year", "New Testament in 30 Days"
+  description String?  @db.Text
+  type        ReadingPlanType @default(PREDEFINED)
+  duration    Int      // Number of days
+  schedule    Json     // Daily reading schedule: {day: 1, readings: [{book, chapter, verses}]}
+  difficulty  String   @default("beginner") // beginner, intermediate, advanced
+  language    String   @default("en")
+  isActive    Boolean  @default(true)
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
+
+  userPlans   UserReadingPlan[]
+
+  @@index([type])
+  @@index([language])
+  @@index([isActive])
+}
+
+enum ReadingPlanType {
+  PREDEFINED
+  CUSTOM
+}
+
+model UserReadingPlan {
+  id              String   @id @default(uuid())
+  userId          String
+  planId          String?  // Null for custom plans
+  name            String   // Plan name (especially for custom plans)
+  startDate       DateTime @default(now())
+  targetEndDate   DateTime // Expected completion date
+  actualEndDate   DateTime? // When actually completed
+  status          ReadingPlanStatus @default(ACTIVE)
+  currentDay      Int      @default(1) // Current day in plan
+  completedDays   Int      @default(0) // Total days completed
+  streak          Int      @default(0) // Current consecutive days
+  longestStreak   Int      @default(0) // Best streak achieved
+  customSchedule  Json?    // For custom plans: same format as ReadingPlan.schedule
+  reminderEnabled Boolean  @default(true)
+  reminderTime    String?  // "08:00" - time of day for reminder
+  createdAt       DateTime @default(now())
+  updatedAt       DateTime @updatedAt
+
+  user            User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+  plan            ReadingPlan? @relation(fields: [planId], references: [id], onDelete: SetNull)
+  progress        UserReadingProgress[]
+
+  @@index([userId])
+  @@index([status])
+  @@index([userId, status])
+}
+
+enum ReadingPlanStatus {
+  ACTIVE
+  COMPLETED
+  PAUSED
+  CANCELLED
+}
+
+model UserReadingProgress {
+  id          String   @id @default(uuid())
+  userId      String
+  userPlanId  String
+  planDay     Int      // Day number in the reading plan
+  date        DateTime @default(now()) // Date of reading
+  bookId      String   // Bible book read
+  chapterNum  Int
+  versesRead  String?  // "1-10" or "all" or null for whole chapter
+  completed   Boolean  @default(true)
+  notes       String?  @db.Text
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
+
+  user        User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+  userPlan    UserReadingPlan @relation(fields: [userPlanId], references: [id], onDelete: Cascade)
+
+  @@unique([userPlanId, planDay, bookId, chapterNum]) // One entry per chapter per day per plan
+  @@index([userId])
+  @@index([userPlanId])
+  @@index([userId, date])
+}