🛡️ Sentinel: [HIGH] Fix overly permissive CORS configuration

[benpiper]

🚨 Severity: HIGH
💡 Vulnerability: The CORS origin configuration accepted unvalidated origins from environment variables, including wildcards (*) and malformed URLs.
🎯 Impact: An attacker could potentially bypass CORS restrictions if a malformed origin is accepted. Furthermore, passing a wildcard * while allow_credentials=True is set causes application errors.
🔧 Fix: Implemented strict URL validation using urllib.parse.urlparse to ensure all origins have a valid http/https scheme and a netloc. Explicitly stripped * from the permitted origins.
✅ Verification: Checked the modified file, updated the Sentinel journal, and ran the backend linter and tests successfully.

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PR created automatically by Jules for task 11364706755739198392 started by @benpiper

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