Fix Docker COPY paths to use absolute destination directories

Dockerfile

@@ -10,8 +10,8 @@ WORKDIR /app
 COPY go.mod go.sum ./
 RUN go mod download
 
-COPY cmd/ ./
-COPY internal ./
+COPY cmd /app/cmd/
+COPY internal /app/internal/
 
 RUN CGO_ENABLED=0 GOOS=linux go build -o /CatsOfMastodonGo ./cmd/CatsOfMastodonBotGo/main.go