docs(README): redesign and update package documentation

- Restructure README content to improve readability and presentation
- Add visually appealing elements like badges and project logo
- Enhance feature description with detailed points and examples
- Consolidate licensing information and link to main project

Author: fulleni

README.md

@@ -1,71 +1,41 @@
-# email_sendgrid
+<div align="center">
+  <img src="https://avatars.githubusercontent.com/u/202675624?s=400&u=dc72a2b53e8158956a3b672f8e52e39394b6b610&v=4" alt="Flutter News App Toolkit Logo" width="220">
+  <h1>Email SendGrid</h1>
+  <p><strong>A concrete implementation of the `EmailClient` interface using the SendGrid API for the Flutter News App Toolkit.</strong></p>
+</div>
 
-![coverage: percentage](https://img.shields.io/badge/coverage-100-green)
-[![style: very good analysis](https://img.shields.io/badge/style-very_good_analysis-B22C89.svg)](https://pub.dev/packages/very_good_analysis)
-[![License: PolyForm Free Trial](https://img.shields.io/badge/License-PolyForm%20Free%20Trial-blue)](https://polyformproject.org/licenses/free-trial/1.0.0)
+<p align="center">
+  <img src="https://img.shields.io/badge/coverage-100%25-green?style=for-the-badge" alt="coverage">
+  <a href="https://flutter-news-app-full-source-code.github.io/docs/"><img src="https://img.shields.io/badge/LIVE_DOCS-VIEW-slategray?style=for-the-badge" alt="Live Docs: View"></a>
+  <a href="https://github.com/flutter-news-app-full-source-code"><img src="https://img.shields.io/badge/MAIN_PROJECT-BROWSE-purple?style=for-the-badge" alt="Main Project: Browse"></a>
+</p>
 
-A concrete implementation of the `EmailClient` interface that uses the SendGrid API to send transactional emails.
+This `email_sendgrid` package provides a concrete implementation of the `EmailClient` interface within the [**Flutter News App Full Source Code Toolkit**](https://github.com/flutter-news-app-full-source-code). It leverages the SendGrid v3 API to send transactional emails, offering a robust and reliable solution for email dispatch. Designed to be used with the `email_repository` and `http_client` packages, it utilizes the standardized `HttpClient` for making HTTP requests and handling errors, ensuring consistent behavior and robust error management. This package is crucial for backend services (like a Dart Frog API) that require integration with a powerful email service provider.
 
-## Description
+## ⭐ Feature Showcase: Reliable SendGrid Email Integration
 
-This package provides `EmailSendGrid`, a class that connects to the SendGrid v3 API to send emails. It is designed to be used with the `email_repository` and `http_client` packages, leveraging the standardized `HttpClient` for making HTTP requests and handling errors.
+This package offers a comprehensive set of features for integrating with the SendGrid API.
 
-## Getting Started
+<details>
+<summary><strong>🧱 Core Functionality</strong></summary>
 
-Add the dependency to your `pubspec.yaml`:
+### 🚀 `EmailClient` Implementation
+- **`EmailSendGrid` Class:** A concrete implementation of the `EmailClient` interface, providing a standardized way to send emails via SendGrid.
+- **SendGrid API Integration:** Connects directly to the SendGrid v3 API for sending transactional emails, ensuring reliable delivery.
 
-```yaml
-dependencies:
-  email_sendgrid:
-    git:
-      url: https://github.com/flutter-news-app-full-source-code/email-sendgrid.git
-      # ref: <specific_tag_or_commit>
-```
+### 🌐 Template-Based Email Sending
+- **`sendTransactionalEmail` Method:** Supports sending emails using pre-defined SendGrid templates, allowing for dynamic content injection via `templateData`. This decouples email content and styling from application logic.
 
-## Usage
+### 🛡️ Integrated Error Handling
+- **`HttpClient` & `HttpException`:** Leverages the `http_client` package for underlying HTTP communication and propagates standardized `HttpException` errors (from `core`), ensuring consistent and predictable error management.
 
-To use this client, you must first configure an `HttpClient` instance with the SendGrid API base URL and an `AuthInterceptor` that provides your SendGrid API key.
+### 💉 Dependency Injection Ready
+- **`HttpClient` Dependency:** Requires an instance of `HttpClient` (from the `http_client` package) configured with the SendGrid API base URL and API key, promoting loose coupling and testability.
 
-```dart
-import 'package:dio/dio.dart';
-import 'package:email_client/email-client.dart';
-import 'package:email_sendgrid/email_sendgrid.dart';
-import 'package:http_client/http_client.dart';
-import 'package:logging/logging.dart';
-
-void main() async {
-  // 1. Configure the HttpClient for SendGrid
-  final sendGridHttpClient = HttpClient(
-    baseUrl: 'https://api.sendgrid.com/v3',
-    tokenProvider: () async => 'YOUR_SENDGRID_API_KEY', // Provide your key here
-    isWeb: false, // Use false for server-side applications
-  );
-
-  // 2. Instantiate the SendGrid email client
-  final EmailClient emailClient = EmailSendGrid(
-    httpClient: sendGridHttpClient,
-    log: Logger('SendGridClient'),
-  );
-
-  // 3. Use the client to send an email
-  try {
-    await emailClient.sendTransactionalEmail(
-      senderEmail: '[email protected]',
-      recipientEmail: '[email protected]',
-      subject: 'Your Subject Here',
-      templateId: 'd-your-template-id',
-      templateData: {'name': 'World'},
-    );
-    print('Email sent successfully!');
-  } on HttpException catch (e) {
-    print('Failed to send email: $e');
-  }
-}
-```
+> **💡 Your Advantage:** This package provides a robust and production-ready SendGrid integration for your email sending needs. It simplifies the process of sending transactional emails, leverages standardized error handling, and integrates seamlessly with the existing `http_client` and `email_client` architecture.
 
+</details>
 
 ## 🔑 Licensing
 
-This package is source-available and licensed under the [PolyForm Free Trial 1.0.0](LICENSE). Please review the terms before use.
-
-For commercial licensing options that grant the right to build and distribute unlimited applications, please visit the main [**Flutter News App - Full Source Code Toolkit**](https://github.com/flutter-news-app-full-source-code) organization.
+This `email_sendgrid` package is an integral part of the [**Flutter News App Full Source Code Toolkit**](https://github.com/flutter-news-app-full-source-code). For comprehensive details regarding licensing, including trial and commercial options for the entire toolkit, please refer to the main toolkit organization page.