Fix: Correct DAST guide factual inaccuracies

[bobbyonmagic]

Fixes factual inaccuracies in PR #940 (DAST Integration guide):

Changes:

1. ✅ British Airways breach (2018): Corrected from "XSS vulnerability" to "Magecart attack (compromised third-party script)" - the actual attack vector
2. ✅ Burp Suite download URL: Updated Linux download instructions to point to releases page with proper version selection instead of invalid direct download URL

Fact-check results:

• ✅ Capital One breach (2019): SSRF, 100M+ records - CORRECT
• ✅ Heartbleed (2014): OpenSSL vulnerability - CORRECT
• ✅ Burp Suite Pro pricing: $449/year - CORRECT
• ✅ OWASP ZAP: Free/open-source, maintained by OWASP Foundation - CORRECT
• ✅ Docker images: ghcr.io/zaproxy/zaproxy:stable - CORRECT
• ✅ CWE numbers: 89 (SQL Injection), 79 (XSS), 22 (Path Traversal), 78 (OS Command Injection) - CORRECT
• ✅ All 4,542 tests passing

Note: This PR should be merged into PR #940 or after PR #940 is merged to main.

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