🛡️ Sentinel: [CRITICAL] Key material not zeroed after use

[igorls]

This PR addresses a critical security vulnerability where sensitive key material (static private keys, shared secrets, chaining keys) was left in memory after a handshake session or when a peer was removed.

Changes:

• Added deinit method to src/wireguard/noise.zig:Handshake which uses std.crypto.secureZero to wipe all sensitive fields.
• Updated deriveTransportKeys in src/wireguard/noise.zig to securely zero ephemeral secrets (chaining_key, hash, remote_ephemeral) immediately after deriving transport keys.
• Modified src/wireguard/device.zig:removePeer to call peer.handshake.deinit() before removing the peer from the peers array, ensuring the memory is scrubbed.
• Added a test case in src/wireguard/noise.zig to verify deinit functionality.
• Updated .jules/sentinel.md with the vulnerability finding and fix.

This ensures that even if memory is dumped or swapped, long-lived secrets are minimized in memory and ephemeral secrets are discarded promptly.

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PR created automatically by Jules for task 5565583968971290168 started by @igorls

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