🛡️ Sentinel: [HIGH] Fix Axum header string literal panic

[google-labs-jules]

🚨 Severity: HIGH
💡 Vulnerability: Application crashes (Denial of Service) when inserting custom headers into Axum HTTP responses using uppercase string literals (e.g., "X-Total-Count").
🎯 Impact: Unhandled crashes if an endpoint receives requests triggering this path, leading to DoS.
🔧 Fix: Updated "X-Total-Count" to "x-total-count" in api/repos.rs to fix the casing.
✅ Verification: Ran cargo check -p gitlawb-node to ensure code compiles correctly.

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PR created automatically by Jules for task 12983494444378466899 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.

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