feat: return GitLab work item comments from issue:show --with-comments

[mglaman]

What changed

drupalorg issue:show <ref> --with-comments now returns the discussion for GitLab work items, not only classic Drupal.org issues. Comments render in text, json, md, and llm output using the same number/author/created/body shape as Drupal.org comments, so agents parse both the same way.

A second, separate commit fixes a pre-existing output bug found while testing: Symfony Console treats <comment> as a built-in style and stripped those tags from every --format=llm response, including the existing Drupal.org comment thread. Formatted output is now written with OUTPUT_RAW.

Why

Closes #374. The AI contribution policy checkpoints merged in #375 tell agents to read the whole thread before writing code. For work item projects the flag was silently ignored, so the skills had to fall back to glab issue view --comments. That fallback is removed here.

How

• GitLab\Client::getIssueNotes() reads the notes endpoint the client already posted slash commands to, following pagination at 100 per page in chronological order.
• New GitLabNote entity. GetGitLabIssueAction takes a $withComments flag and drops system: true notes, matching the Drupal.org path that drops "System Message" comments. Replies from drupalbot are dropped too by default, because the work item's labels and assignees already reflect what the bot confirms. --include-bot-comments brings them back.
• GitLabIssueResult carries comments, serialized under a comments key in JSON.
• issue:show reads the flag before branching on ref type and renders comments in text mode for work items.
• Skill text: the glab fallback is gone from the policy reference and the work-on-issue skill, and the main skill no longer says the flag is Drupal.org-only.

Testing notes

• vendor/bin/phpunit: 219 tests pass. New GetGitLabIssueActionTest covers no notes request without the flag, system and bot note filtering, the --include-bot-comments opt-in, and JSON shape. Formatter tests cover the <comments> element and ## Comments heading, present and absent.
• vendor/bin/phpcs src and vendor/bin/phpstan analyse src clean.
• Live: php drupalorg issue:show ai_context#3586157 --with-comments --format=llm returns 14 comments, or 17 with --include-bot-comments; without --with-comments, none. php drupalorg issue:show 3383637 --with-comments --format=llm now shows the <comment> wrapper on all 16 Drupal.org comments, which it did not before the raw-output fix.

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