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.

database/schema/schema.sql

@@ -16,6 +16,22 @@ INSERT INTO library_types (name, description, allowed_extensions) VALUES
 ('comics', 'Comic book archives and image formats', ARRAY['.cbz', '.cbr', '.cb7', '.cbt', '.pdf']),
 ('manga', 'Manga files including archives and image folders', ARRAY['.cbz', '.cbr', '.png', '.jpg', '.jpeg', '.gif', '.bmp', '.webp']);
 
+-- Create users table
+CREATE TABLE users (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    email VARCHAR(255) UNIQUE NOT NULL,
+    username VARCHAR(255) UNIQUE NOT NULL,
+    password_hash VARCHAR(255) NOT NULL,
+    first_name VARCHAR(255),
+    last_name VARCHAR(255),
+    role VARCHAR(20) NOT NULL DEFAULT 'user' CHECK (role IN ('admin', 'user')),
+    theme VARCHAR(50) DEFAULT 'tokyo-night',
+    scan_frequency_minutes INTEGER DEFAULT 60,
+    auto_scan_enabled BOOLEAN DEFAULT true,
+    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
+    updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
+);
+
 -- Create libraries table
 CREATE TABLE libraries (
     id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
@@ -47,22 +63,6 @@ CREATE TABLE library_visibility (
     UNIQUE(user_id, library_id)
 );
 
--- Create users table
-CREATE TABLE users (
-    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
-    email VARCHAR(255) UNIQUE NOT NULL,
-    username VARCHAR(255) UNIQUE NOT NULL,
-    password_hash VARCHAR(255) NOT NULL,
-    first_name VARCHAR(255),
-    last_name VARCHAR(255),
-    role VARCHAR(20) NOT NULL DEFAULT 'user' CHECK (role IN ('admin', 'user')),
-    theme VARCHAR(50) DEFAULT 'tokyo-night',
-    scan_frequency_minutes INTEGER DEFAULT 60,
-    auto_scan_enabled BOOLEAN DEFAULT true,
-    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
-    updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
-);
-
 -- Create media_items table (replaces ebooks table for broader media support)
 CREATE TABLE media_items (
     id UUID PRIMARY KEY DEFAULT gen_random_uuid(),