feat(GitLab): Link GitLab issues and merge requests to feature flags

[emyller]

• I have read the Contributing Guide.
• I have added information to docs/ if required so people know about the feature.
• I have filled in the "Changes" section below.
• I have filled in the "How did you test this code" section below.

Changes

Closes #7160

Stack: #7270 (backend) → #7273 (frontend) → #7274 (this)

With browsing in place (#7270, #7273), users can now link GitLab issues and merge requests to their feature flags. This completes the core linking flow.

Slight refactor: <ExternalResourcesTable> now renders regardless of GitHub.

Review effort: 2/5

How did you test this code?

Integration tests. Manual UI tests. Screenshots:

[vercel]

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Project	Deployment	Actions	Updated (UTC)
flagsmith-frontend-preview	Ready	Preview, Comment	Apr 20, 2026 10:39pm
flagsmith-frontend-staging	Ready	Preview, Comment	Apr 20, 2026 10:39pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Ignored	Preview	Apr 20, 2026 10:39pm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.37%. Comparing base (fc564c4) to head (7649dbc).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7274   +/-   ##
=======================================
  Coverage   98.37%   98.37%           
=======================================
  Files        1364     1366    +2     
  Lines       51071    51161   +90     
=======================================
+ Hits        50239    50328   +89     
- Misses        832      833    +1     

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[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-e2e:pr-7274	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api-test:pr-7274	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api:pr-7274	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-7274	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-7274	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-frontend:pr-7274	Finished ✅	Results ✅

[emyller]

Note

This code is moved from frontend/web/components/ExternalResourcesLinkTab.tsx, only because we needed to extract ExternalResourcesTable out of ExternalResourcesLinkTab. Minor uncoupling necessary, but no improvements in this pull request.

[claude]

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