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>

internal/store/store_test.go

@@ -16,11 +16,11 @@ func TestRoundTrip(t *testing.T) {
 	defer st.Close()
 
 	msg := &proto.ChatMessage{
-		Mid:    "aabbccdd00112233",
-		From:   proto.PeerID("deadbeef"),
-		Room:   "general",
-		Body:   "hello world",
-		SentAt: time.Now().UTC().Truncate(time.Second),
+		Mid:  "aabbccdd00112233",
+		From: proto.PeerID("deadbeef"),
+		Room: "general",
+		Text: "hello world",
+		Ts:   time.Now().UTC().Truncate(time.Second).UnixMilli(),
 	}
 
 	if err := st.SaveMessage(msg); err != nil {
@@ -40,7 +40,7 @@ func TestRoundTrip(t *testing.T) {
 		t.Fatalf("got %d messages, want 1", len(msgs))
 	}
 	got := msgs[0]
-	if got.Mid != msg.Mid || got.Body != msg.Body || got.Room != msg.Room {
+	if got.Mid != msg.Mid || got.Text != msg.Text || got.Room != msg.Room {
 		t.Fatalf("message mismatch: %+v", got)
 	}
 }
@@ -79,11 +79,11 @@ func TestRecentMessagesOrdering(t *testing.T) {
 	base := time.Now().UTC().Truncate(time.Second)
 	for i := range 5 {
 		st.SaveMessage(&proto.ChatMessage{
-			Mid:    string(rune('a'+i)) + "000000000000000",
-			From:   "deadbeef",
-			Room:   "general",
-			Body:   string(rune('a' + i)),
-			SentAt: base.Add(time.Duration(i) * time.Second),
+			Mid:  string(rune('a'+i)) + "000000000000000",
+			From: "deadbeef",
+			Room: "general",
+			Text: string(rune('a' + i)),
+			Ts:   base.Add(time.Duration(i) * time.Second).UnixMilli(),
 		})
 	}
 
@@ -96,7 +96,7 @@ func TestRecentMessagesOrdering(t *testing.T) {
 	}
 	// Must be oldest-first.
 	for i := 1; i < len(msgs); i++ {
-		if msgs[i].SentAt.Before(msgs[i-1].SentAt) {
+		if msgs[i].Ts < msgs[i-1].Ts {
 			t.Fatalf("messages not in ascending order at index %d", i)
 		}
 	}