fix(gitlab): list required fine-grained permissions and surface login errors

[afonsojramos]

Summary

• The GitLab personal access token login hint now names the fine-grained permissions the login actually needs, Todo (read, update) and User (read), instead of claiming the Todo resource alone is enough; Metadata and Personal Access Token (read) remain optional and only feed the instance version and scope display on the Accounts page.
• The token validation failure banner shows the underlying error on a second line (first line only, capped at 150 characters, non-Error rejections skipped), so a 403 from a token that lacks permissions is visible instead of only the generic message.
• GitLab API error messages no longer end in a trailing space when an HTTP/2 response carries no reason phrase.
• The redundant "on your GitLab instance to create a token" caption is removed from the GitLab form and the shared form prop is now optional, with the snapshot and visual baselines regenerated.

Closes #3252

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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