Add "Why Kafka and Karafka" documentation page

[mensfeld]

Summary

• Adds a new Why Kafka and Karafka page explaining why teams choose Kafka over simpler alternatives (Sidekiq, RabbitMQ, SQS) and how Karafka makes Kafka a first-class citizen in Ruby/Rails
• Covers core concepts (event log vs queue), a comparison table, key capabilities, decoupling benefits, when Kafka is/isn't the right choice, Kafka Queues (KIP-932), and the Karafka ecosystem
• Includes 6 practical use cases with code samples: marketplace order fan-out, Stripe webhook ingestion, ordered profile updates, fraud detection with delayed processing, HIPAA audit trails, and product listing decoupling
• Links the new page from Home.md under Basics

Test plan

• Verify npm run lint passes
• Verify ./bin/mklint passes
• Review use cases and code samples for accuracy
• Check all internal wiki links resolve correctly
• Check all external image URLs load

[Copilot]

Pull request overview

Adds a new introductory documentation page explaining when Kafka is a good fit (vs queue-oriented systems) and how Karafka fits into Ruby/Rails architectures, and links it from the docs home page.

Changes:

• Introduces a new “Why Kafka and Karafka” guide covering Kafka’s event-log model, key capabilities, and practical Rails-oriented use cases.
• Adds the new page to the “Basics” section in Home.md for discoverability.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Why-Kafka-and-Karafka.md	New conceptual + practical overview page comparing Kafka to common Ruby messaging alternatives and positioning Karafka/WaterDrop/Web UI.
Home.md	Adds a navigation entry pointing to the new page under Basics.

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