v0.0.7: Chunked encrypted file transfer

Protocol:
- WireMessage::FileHeader { id, sender_fp, filename, file_size, total_chunks, sha256 }
- WireMessage::FileChunk { id, sender_fp, filename, chunk_index, total_chunks, data }
- 64KB chunks, SHA-256 integrity verification

CLI TUI:
- /file <path> command: reads file, chunks, encrypts each with ratchet, sends
- Progress display: "Sending file.pdf [3/10]..."
- Incoming file reassembly with chunk tracking
- SHA-256 verification on complete
- Saves to data_dir/downloads/
- Max file size: 10MB

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

warzone/crates/warzone-client/Cargo.toml

@@ -24,6 +24,7 @@ hex.workspace = true
 base64.workspace = true
 x25519-dalek.workspace = true
 bincode.workspace = true
+sha2.workspace = true
 libc = "0.2"
 uuid.workspace = true
 chrono.workspace = true