Decode the API's actual fields in neoirc-cli (closes #146)

The CLI read the poll cursor from `lastId` while the server sends
`last_id`, so the cursor stayed at 0 and every poll returned the
whole queue at once. It now reads `last_id`.

/names decodes the member objects the server sends and prints each
nick with `@` for an operator or `+` for a voiced member. /list
prints each channel's name and topic, since the server sends no
member count. StateResponse.Channels decodes channel objects.

/topic with no text prints a usage line and sends nothing, because
the HTTP API has no topic query and a TOPIC without text gets 461.
The help says "Set topic".

The client tests serve the bodies the handlers send, so a wrong JSON
tag in types.go fails a test; another test covers the /names prefixes.

Model: opus-5-5

internal/cli/app_internal_test.go

@@ -0,0 +1,51 @@
+package cli
+
+import (
+	"testing"
+
+	api "sneak.berlin/go/neoirc/internal/cli/api"
+)
+
+func TestMemberPrefix(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name   string
+		member api.Member
+		want   string
+	}{
+		{
+			name:   "operator",
+			member: api.Member{Nick: "alice", IsOperator: true},
+			want:   "@",
+		},
+		{
+			name:   "voiced member",
+			member: api.Member{Nick: "bob", IsVoiced: true},
+			want:   "+",
+		},
+		{
+			name: "voiced operator",
+			member: api.Member{
+				Nick: "Carol", IsOperator: true, IsVoiced: true,
+			},
+			want: "@",
+		},
+		{
+			name:   "plain member",
+			member: api.Member{Nick: "dave"},
+			want:   "",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+
+			got := memberPrefix(test.member)
+			if got != test.want {
+				t.Fatalf("got %q, want %q", got, test.want)
+			}
+		})
+	}
+}