Bring wire protocol into full YAW/2 spec compliance

Five interop issues fixed against PROTOCOL.md:

- Join signature now covers nonce_raw || net_ascii (64-char UTF-8 hex
  string) as specified in §5.1, not net_raw_bytes. Both anchor server
  and client updated to match.

- Chat wire fields renamed to spec names: text/ts (Unix ms int64)
  replacing body/sent_at (ISO timestamp). Flat layout on PeerMessage
  matches §8 exactly; store and TUI updated accordingly.

- Direct messages now use the spec "pm" type (flat {type,mid,text,ts})
  instead of chat+to. Receiver reconstructs a ChatMessage with
  dm:<short-id> room for IPC/storage. §8 compliant.

- File transfer message types changed to spec hyphenated names:
  file-offer, file-accept, file-cancel, file-done with spec field
  names (name/size not filename/size_bytes). §9 compliant.

- DataChannel open-race (§14 gotcha #3) fixed with sync.Once: doOpen
  fires on OnOpen callback or immediately if the channel is already
  open when WireDataChannel is called (answerer race).

Also fixes two bugs found during testing:

- mid was missing from outgoing wire messages, causing all received
  messages to arrive with mid="" and collide on the UNIQUE DB
  constraint. mid is now included on all sent chat/pm messages; a
  random mid is generated for any received message that omits it.

- Test scripts hardened: kill -9 + active lsof polling replaces blind
  sleep for port cleanup; join_network sent before peer_field queries
  (local_peer is now network-scoped and nil until joined).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test-tui.sh

@@ -19,6 +19,19 @@ CYAN='\033[0;36m'; DIM='\033[2m'; BOLD='\033[1m'; RESET='\033[0m'
 rm -rf "$DATA_ROOT"
 mkdir -p "$DATA_ROOT/bin"
 
+# Kill any leftover processes holding our fixed ports.
+for port in "$ANCHOR_PORT" "$ALICE_IPC" "$BOB_IPC" "$CHARLIE_IPC"; do
+    pid=$(lsof -ti tcp:"$port" 2>/dev/null || true)
+    [ -n "$pid" ] && kill -9 $pid 2>/dev/null || true
+done
+for port in "$ANCHOR_PORT" "$ALICE_IPC" "$BOB_IPC" "$CHARLIE_IPC"; do
+    n=0
+    while lsof -ti tcp:"$port" >/dev/null 2>&1; do
+        sleep 0.1; n=$(( n + 1 ))
+        [ "$n" -gt 30 ] && break
+    done
+done
+
 PIDS=()
 cleanup() {
     for pid in "${PIDS[@]:-}"; do