Clean project layout and fix release workflow

internal/app/join_leave_events_test.go

@@ -0,0 +1,26 @@
+package app
+
+import (
+	"testing"
+	"time"
+)
+
+func TestDeduplicateJoinLeaveEventsIgnoresRepeatedReplays(t *testing.T) {
+	at := time.Date(2026, 7, 1, 1, 23, 45, 0, time.FixedZone("JST", 9*60*60))
+	events := []JoinLeaveEvent{
+		{At: at, Kind: "join", Name: "Alice", Count: 10},
+		{At: at, Kind: "join", Name: "Alice", Count: 11},
+		{At: at.Add(5 * time.Second), Kind: "leave", Name: "Alice", Count: 9},
+	}
+
+	got := dedupeJoinLeaveEvents(events)
+	if len(got) != 2 {
+		t.Fatalf("expected 2 unique events, got %d: %#v", len(got), got)
+	}
+	if got[0].Count != 10 {
+		t.Fatalf("expected first event to remain stable, got %#v", got[0])
+	}
+	if got[1].Kind != "leave" {
+		t.Fatalf("expected leave event to remain, got %#v", got[1])
+	}
+}