Feat/gitlab mr metrics

[Akanksha-020]

Summary

Add optional GitLab MR analytics to PR Metrics (API + UI), with pagination and caching.
Closes #11

Note: GitLab stats appear only when session.gitlabToken is present (depends on GitLab OAuth PR).

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup

Changes Made

• Add GitLab MR fetch with pagination and caching in PR metrics API
• Return optional gitlab metrics alongside GitHub stats when token is present
• Render a GitLab MR section + donut chart in PR Analytics UI

How to Test

Steps for the reviewer to verify this works:

1. Load the dashboard without a GitLab token; PR Analytics shows GitHub-only stats.
2. With a GitLab token in session, hit /api/metrics/prs?refresh=1 and confirm GitLab stats render.
3. Verify pagination by checking a user with >100 MRs (if available).

Screenshots (if UI change)

N/A

Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff
• Added/updated tests if applicable

[vercel]

@Akanksha-020 is attempting to deploy a commit to the PRIYANSHU DOSHI's projects Team on Vercel.

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus