fix: reconcile the issues stream and remove the legacy output shims

Use one canPrompt and pullNumberArguments for the comment commands, set
display preferences instead of the retired environment variables in
tests, and delete writeList, writeItem, batch, table, writeRecord(s),
the legacy column map, confirm, require, validateMilestoneFlags and
listWindow now that every command uses their replacements.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/comments_test.go

@@ -33,6 +33,7 @@ func TestCommentConfirmationNamesTheTarget(t *testing.T) {
 	defer server.Close()
 	deps, out, diagnostics := serverDeps(t, server.URL)
 	deps.Getenv = serverEnv(server.URL, map[string]string{"NO_COLOR": "1"})
+	plainOutput(t, deps)
 	prompt := &scriptedPrompter{accept: true, input: "Prompted"}
 	deps.Prompter = prompt
 	deps.Streams.InTTY, deps.Streams.ErrTTY, deps.Streams.OutTTY = true, true, true
@@ -160,7 +161,8 @@ func TestCommentGroupCommentsLikeGh(t *testing.T) {
 		"id:\t80\nauthor:\tbob\ncreated_at:\t2026-10-11T19:00:00Z\nurl:\t\n--\nSecond\nline\n--\n"+
 		"id:\t81\nauthor:\tbob\ncreated_at:\t2026-10-11T19:10:00Z\nurl:\t\n--\nThird\n--\n", out.String())
 	deps.Streams.OutTTY = true
-	deps.Getenv = serverEnv(server.URL, map[string]string{"NO_COLOR": "1", "TEA_MARKDOWN": "raw"})
+	deps.Getenv = serverEnv(server.URL, map[string]string{"NO_COLOR": "1"})
+	plainOutput(t, deps)
 	require.NoError(t, run("issue", "comment", "list", "1"))
 	require.Equal(t, "#79  alice • about 2 hours ago\n  First **one**\n\n"+
 		"#80  bob • about 1 hour ago (edited)\n  Second\n  line\n\n"+