fix(cmdutils): show error text as written

Description

glab capitalizes the first word of every error message. This breaks text where case matters: flags (--Title, '--Stdin'), acronyms (JSON becomes Json), config keys and paths.

This happens in a terminal, and also when stderr is not a terminal (CI logs, scripts, stderr sent to a file).

Now glab shows the error text exactly as written, in both cases.

At first I only skipped the capital letter for errors that start with -. That still broke quoted flags like '--stdin' and acronyms, so now no error text is changed.

One decision for you:

1. Errors that start with a normal word no longer get a capital first letter. For example, could not prompt: ... instead of Could not prompt: .... Scripts that match the old capitalized text will see the lowercase word too. Is this ok? If not, I can keep the capital letter only for errors that start with a lowercase letter.

Related Issues

Closes #8619

How has this been tested?

I built glab from main (glab-main) and from this branch (glab-8619), and ran glab auth login with a temp HOME and GLAB_CONFIG_DIR:

$ GLAB_NO_PROMPT=true CLICOLOR_FORCE=1 script -q -c "./glab-main auth login" /dev/null
   ERROR

  '--Stdin', '--token', '--job-token', '--web', or '--device' required when not running interactively.

$ GLAB_NO_PROMPT=true CLICOLOR_FORCE=1 script -q -c "./glab-8619 auth login" /dev/null
   ERROR

  '--stdin', '--token', '--job-token', '--web', or '--device' required when not running interactively.

The same happens with stderr sent to a file:

$ ./glab-main snippet create note.txt 2>err-main.txt
$ cat err-main.txt
   ERROR

  --Title required for snippets.

$ ./glab-8619 snippet create note.txt 2>err-8619.txt
$ cat err-8619.txt
   ERROR

  --title required for snippets.

This is the visible effect from decision 1:

$ CLICOLOR_FORCE=1 script -q -c "./glab-main auth login </dev/null" /dev/null
   ERROR

  Could not prompt: huh: bubbletea: could not create cancelable reader: add reader to epoll interest list.

$ CLICOLOR_FORCE=1 script -q -c "./glab-8619 auth login </dev/null" /dev/null
   ERROR

  could not prompt: huh: bubbletea: could not create cancelable reader: add reader to epoll interest list.

I added tests for a long flag, a short flag, a quoted flag list, a flag in backticks, an acronym and a normal sentence. The new tests fail without the fix.

$ GOFLAGS=-p=2 go test -count=1 ./internal/cmdutils/
ok  	gitlab.com/gitlab-org/cli/internal/cmdutils	2.226s

The rest runs in the pipeline.

Implemented with AI assistance; I reviewed and tested the changes.