🛡️ Sentinel: [HIGH] Fix DoS vulnerability from uppercase header

[google-labs-jules]

🚨 Severity: HIGH
💡 Vulnerability: DoS via runtime panic caused by an uppercase character in a string literal used as an axum header name. Axum's HeaderMap::insert requires string literals to be completely lowercase (or use predefined constants), and uppercase strings cause a panic during IntoHeaderName conversion.
🎯 Impact: An attacker could potentially cause the server to panic and crash by triggering code paths that insert this header, leading to a Denial of Service (DoS).
🔧 Fix: Changed "X-Total-Count" to "x-total-count" in crates/gitlawb-node/src/api/repos.rs.
✅ Verification: Verified by checking that cargo check and cargo clippy pass successfully with the updated code. Added .jules/sentinel.md entry.

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PR created automatically by Jules for task 9048846044558508548 started by @euxaristia

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[github-actions]

Thanks for the contribution. A couple of things will help us review this faster:

• Link the issue this addresses (Closes #123). For protocol changes, open an issue first.
• This changes Rust source but no tests changed. Tests are required for fixes and strongly encouraged for features.

See CONTRIBUTING.md. Update the PR and these notes will clear automatically.