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-wasm/src/lib.rs

@@ -448,5 +448,11 @@ pub fn decrypt_wire_message(
                 "receipt_type": rt_str,
             }).to_string())
         }
+        _ => {
+            // File transfer messages not yet handled in WASM
+            Ok(serde_json::json!({
+                "type": "unsupported",
+            }).to_string())
+        }
     }
 }