docs(readme): revert HTML anchor tags back to Markdown links

## Starting point
We attempted to force external links in the README to open in a new tab by using HTML `<a>` tags with `target="_blank"`. However, this didn't work on GitHub.

## Investigation
Web research confirms that GitHub's Markdown renderer intentionally strips the `target="_blank"` attribute from both Markdown extensions and raw HTML for security reasons. There is no native support or workaround for forcing links to open in a new tab within a GitHub README as of 2026.

## Changes made
Reverted the HTML anchor tags back to standard Markdown links (`[text](url)`) for cleaner syntax:
- Restored `pyventus` and `fastapi-events` links in the "Consider alternatives if" section
- Restored links in the Comparison table header

## Result
Links use the clean Markdown syntax again. Users will need to use their browser's native functionality (Ctrl+click / Cmd+click / Middle-click) to open external links in new tabs.

Author: FirstUnicorn

README.md

@@ -53,8 +53,8 @@ from messaging.infrastructure import SqlAlchemyOutboxRepository
 - Native broker integration (FastStream, Debezium CDC, RabbitMQ DLX)
 
 **Consider alternatives if:**
-- Simple in-process events only → <a href="https://github.com/mdapena/pyventus" target="_blank">`pyventus`</a>
-- FastAPI request-scoped events → <a href="https://github.com/melvinkcx/fastapi-events" target="_blank">`fastapi-events`</a>
+- Simple in-process events only → [`pyventus`](https://github.com/mdapena/pyventus)
+- FastAPI request-scoped events → [`fastapi-events`](https://github.com/melvinkcx/fastapi-events)
 - Non-Kafka message brokers without CDC support
 - No need for durable outbox persistence
 
@@ -64,7 +64,7 @@ Support scale: `❌` none, `✅` basic, `✅✅` strong, `✅✅✅` first-class
 
 `python-eventing` prioritizes **durable messaging** (transactional outbox + CDC) and **Kafka/RabbitMQ integration** over in-process event simplicity:
 
-| Capability | `python-eventing` | <a href="https://github.com/mdapena/pyventus" target="_blank">`pyventus`</a> | <a href="https://github.com/melvinkcx/fastapi-events" target="_blank">`fastapi-events`</a> | Notes |
+| Capability | `python-eventing` | [`pyventus`](https://github.com/mdapena/pyventus) | [`fastapi-events`](https://github.com/melvinkcx/fastapi-events) | Notes |
 | --- | --- | --- | --- | --- |
 | Transactional outbox | ✅✅✅ | ❌ | ❌ | Durable local DB plus outbox boundary is a core feature here |
 | Kafka data plane | ✅✅✅ | ❌ | ❌ | This package is built for Kafka-backed microservice messaging |