fix: prevent RCE in openURLMiddleware via URL sanitization

[Copilot]

Addresses CVE-2025-11953: URLs passed to the /open-url endpoint were forwarded directly to open(), enabling command injection on Windows via shell metacharacters.

Changes

• Add strict-url-sanitise dependency for security-focused URL validation
• Sanitize URLs before passing to open(), rejecting malformed or malicious input with HTTP 400
• Add test coverage for known attack vectors

Test cases

'https://www.$(calc.exe).com/foo'  // Command substitution in hostname
'https://evil.com?|calc.exe'       // Windows pipe separator
'https://example.com/?a=%¾TA%'     // Env var exfiltration (%BETA%)

Original prompt

Reattempt #2735 using the strict-url-sanitise npm package. Parsing errors should be surfaced on the HTTP endpoint and fail.

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[huntie]

@thymikee Ready for review. This is a heavily steered Copilot diff!

• Uses strict-url-sanitise (190k weekly, manually code inspected).
  • Rejects URLs with any shell metacharacters.
  • Avoids us from maintaining a granular implementation in this codebase.
• Local tests covering all cases mentioned in fix: RCE vulnerability from CVE-2025-11953 #2735.