Add standard security headers (HSTS, CSP, etc.)

[google-labs-jules]

Implemented standard security headers in the HTTP transport layer to improve the application's security posture.

Security Enhancements:

• X-Content-Type-Options: nosniff: Prevents browsers from trying to guess the MIME type, reducing the risk of drive-by download attacks.
• X-Frame-Options: DENY: Prevents the application from being embedded in iframes, mitigating clickjacking attacks.
• Content-Security-Policy: Sets default-src 'none', strictly blocking all external resources and inline scripts. This is appropriate for an API-only service and significantly reduces XSS risks.
• Strict-Transport-Security (HSTS): Enforces HTTPS usage by browsers for 1 year (max-age=31536000), including subdomains. This is applied conditionally: only when the request is secure (HTTPS) or the environment is production, preventing issues during local development.

Verification:

• Added a temporary test file src/security-headers.test.ts which verified the presence and correctness of all headers.
• Verified that existing functionality (CORS, API endpoints) remains unaffected by running the full test suite (npm test).
• Confirmed that HSTS is not applied on non-secure local connections, ensuring developer experience is not degraded.

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PR created automatically by Jules for task 3274137449072602053 started by @davidruzicka

[google-labs-jules]

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[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/http-transport.ts	77.77%	2 Missing ⚠️

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