Wire E2E messaging: send, recv, session persistence, auto-registration

CLI client (warzone):
- `warzone init` now generates pre-key bundle (1 SPK + 10 OTPKs),
  stores secrets in local sled DB, saves bundle for server registration
- `warzone register -s <url>` registers bundle with server
- `warzone send <fp> <msg> -s <url>` full E2E flow:
  - Auto-registers bundle on first use
  - Fetches recipient's pre-key bundle
  - Performs X3DH key exchange (first message) or uses existing session
  - Encrypts with Double Ratchet
  - Sends WireMessage envelope to server
- `warzone recv -s <url>` polls and decrypts:
  - Handles KeyExchange messages (X3DH respond + ratchet init as Bob)
  - Handles Message (decrypt with existing ratchet session)
  - Saves session state after each decrypt

Wire protocol (WireMessage enum):
- KeyExchange variant: sender identity, ephemeral key, OTPK id, ratchet msg
- Message variant: sender fingerprint + ratchet message

Session persistence:
- Ratchet state serialized with bincode, stored in sled (~/.warzone/db)
- Pre-key secrets stored in sled, OTPKs consumed on use
- Sessions keyed by peer fingerprint

Networking (net.rs):
- register_bundle, fetch_bundle, send_message, poll_messages
- JSON API over HTTP, bundles serialized with bincode + base64

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

warzone/Cargo.lock

@@ -2557,7 +2557,10 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "argon2",
+ "base64",
+ "bincode",
  "chacha20poly1305",
+ "chrono",
  "clap",
  "crossterm",
  "hex",
@@ -2570,7 +2573,9 @@ dependencies = [
  "tokio",
  "tracing",
  "tracing-subscriber",
+ "uuid",
  "warzone-protocol",
+ "x25519-dalek",
  "zeroize",
 ]