v0.0.13: Sender Keys for efficient group encryption

Protocol (sender_keys.rs):
- SenderKey: symmetric key with chain ratchet (forward secrecy per chain)
- generate(), rotate(), encrypt(), decrypt()
- SenderKeyDistribution: share key via 1:1 encrypted channel
- SenderKeyMessage: encrypted group message (O(1) instead of O(N))
- Chain key ratchets forward on each message (HKDF)
- Generation counter for key rotation tracking
- 4 tests: basic, multi-message, rotation, old-key rejection

WireMessage:
- GroupSenderKey variant: encrypted group message
- SenderKeyDistribution variant: key sharing

Server: dedup handles new variants.
CLI TUI + recv: stub handlers for new message types.
23/23 protocol tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

warzone/crates/warzone-protocol/src/lib.rs

@@ -10,3 +10,4 @@ pub mod message;
 pub mod session;
 pub mod store;
 pub mod history;
+pub mod sender_keys;