feat: add highlights and notes annotation system

This major update implements a complete user annotation system:

## 🎯 New Features
- User notes with position tracking for media items
- Text highlighting with customizable colors
- Highlight-note associations for detailed annotations
- Full CRUD API for both notes and highlights
- Backward compatibility with existing ebook endpoints

## 📊 Database Changes
- Add media_notes table (id, media_item_id, user_id, content, position, timestamps)
- Add media_highlights table (id, media_item_id, user_id, selection_text, start/end_position, color, optional note_id)
- Add foreign key relationships with CASCADE deletes
- Add proper indexes for performance
- Add database schema views for ebook backward compatibility

## 🔧 API Implementation
- Complete REST API endpoints for notes and highlights
- JWT authentication with proper middleware bypass
- Request validation with meaningful error responses
- UUID validation and type safety
- Support for hex color codes in highlights

## 🧪 Testing & Documentation
- Comprehensive test suite covering authentication scenarios
- Bruno API collection for manual testing
- Detailed testing guide with troubleshooting
- Updated documentation in README and TESTING.md

## 📁 Backward Compatibility
- Existing ebook endpoints continue working
- Database views maintain API contracts
- No breaking changes for existing integrations

The annotation system is now fully functional and ready for production use.

cmd/server/main.go

@@ -6,6 +6,7 @@ import (
 	"bookmann/internal/handlers"
 	"bookmann/templates"
 	"bytes"
+	"context"
 	"log"
 	"net/http"
 
@@ -13,6 +14,7 @@ import (
 	"github.com/golang-jwt/jwt/v5"
 	"github.com/google/uuid"
 	"github.com/jackc/pgx/v5/pgtype"
+	"github.com/jackc/pgx/v5/pgxpool"
 	"github.com/labstack/echo-jwt/v4"
 	"github.com/labstack/echo/v4"
 	"github.com/labstack/echo/v4/middleware"
@@ -30,7 +32,7 @@ func (cv *CustomValidator) Validate(i interface{}) error {
 func main() {
 	cfg := config.LoadConfig()
 
-	dbPool, err := database.NewConnection(cfg.DatabaseURL())
+	dbPool, err := pgxpool.New(context.Background(), cfg.DatabaseURL())
 	if err != nil {
 		log.Fatal("Failed to connect to database:", err)
 	}