Complete tasks 3.2-3.3: Data models and DynamoDB table schemas

- Defined all 8 data models (Page, Widget, Bookmark, Note, TagAssociation, Group, Share, Preferences)
- Implemented DynamoDB table creation for all tables with proper schemas
- Added GSIs for efficient querying (UserBookmarksIndex, UserNotesIndex, TagItemsIndex, UserSharesIndex)
- Comprehensive test coverage for all table schemas
- Updated init-db command to create all tables

cmd/init-db/main.go

@@ -22,12 +22,34 @@ func main() {
 		log.Fatalf("Failed to create DynamoDB client: %v", err)
 	}
 
-	log.Println("Creating Users table...")
-	if err := db.CreateUsersTable(ctx); err != nil {
-		log.Fatalf("Failed to create Users table: %v", err)
+	// Create all tables
+	tables := []struct {
+		name   string
+		create func(context.Context) error
+	}{
+		{"Users", db.CreateUsersTable},
+		{"Pages", db.CreatePagesTable},
+		{"Widgets", db.CreateWidgetsTable},
+		{"Bookmarks", db.CreateBookmarksTable},
+		{"Notes", db.CreateNotesTable},
+		{"TagAssociations", db.CreateTagAssociationsTable},
+		{"Groups", db.CreateGroupsTable},
+		{"SharedItems", db.CreateSharedItemsTable},
+		{"Preferences", db.CreatePreferencesTable},
+	}
+
+	for _, table := range tables {
+		log.Printf("Creating %s table...", table.name)
+		if err := table.create(ctx); err != nil {
+			log.Fatalf("Failed to create %s table: %v", table.name, err)
+		}
+		log.Printf("✓ %s table created successfully", table.name)
 	}
-	log.Println("✓ Users table created successfully")
 
 	fmt.Println("\nDatabase initialization complete!")
+	fmt.Println("All tables created:")
+	for _, table := range tables {
+		fmt.Printf("  - %s\n", table.name)
+	}
 	os.Exit(0)
 }