feat(tasks): import issues from GitLab

[leoisadev1]

Summary

Gitpay can import GitHub and Bitbucket issues. This adds GitLab.com so a URL like https://gitlab.com/mission-center-devs/mission-center/-/issues/3 (the example on #1097) creates a task.

What changed

• Parse gitlab.com / www.gitlab.com issue URLs, including nested groups, /-/issues/:id, and /-/work_items/:id
• GitlabConnect client for the public REST API (/projects/:path/issues/:iid, project metadata, languages)
• Map GitLab opened to gitpay open and description to the issue body the UI already expects
• GitLab button on both import dialogs; pasting a gitlab.com URL selects GitLab

Tests

Mocha coverage of the parser plus a nock of the shipped GitlabConnect client (12 passing).

Closes #1097

[alexanmtz]

Thanks for this — the GitLab connector and the import-side work here is a good start, and the title/status sync-on-fetch is genuinely well done.

It's not mergeable as-is yet, though. Two things need to land first:

1. Claiming is hardcoded to GitHub only — taskClaim.ts rejects any task where task.provider !== 'github'. As it stands, a GitLab bounty could be imported and funded but never claimed or paid out.
2. There's no GitLab identity/connector yet to verify "the person claiming this bounty is the same person the issue belongs to on GitLab" — that requires either a dedicated OAuth strategy or a schema change, and depends on what GitLab's auth model actually supports (it does have standard OAuth2 apps, so this looks feasible).

On top of that, taskBuilds.ts/taskFetch.ts are growing a large duplicated switch case per provider with no shared interface — we'd like to settle a shared provider-registry shape before adding more cases in that pattern.

We've opened #1563 to work through all of this, and are asking in #1097 for provider-specific verification on the identity/OAuth side. Could you hold off on further work here until that's settled, so effort isn't spent on a shape that ends up changing? We'll follow up on this PR once the architecture discussion lands.