feat(similarity): add Worker skeleton with constructor + Run loop

internal/similarity/worker_test.go

@@ -0,0 +1,22 @@
+package similarity
+
+import (
+	"io"
+	"log/slog"
+	"testing"
+	"time"
+)
+
+func TestNewWorker_DefaultsMatchSpec(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+	w := NewWorker(nil, nil, logger)
+	if w.tick != 1*time.Hour {
+		t.Errorf("tick = %v, want 1h", w.tick)
+	}
+	if w.batch != 5 {
+		t.Errorf("batch = %d, want 5", w.batch)
+	}
+	if w.topK != 20 {
+		t.Errorf("topK = %d, want 20", w.topK)
+	}
+}