fix: detect merged PRs to externally-owned repos for open source scoring

[janampatel]

Problem

Open source scoring only ever looks at repos the candidate owns (GET /users/{username}/repos), and classifies open_source vs self_project by whether other people contributed to those repos. It never checks whether the candidate contributed to someone else's repo, which is what open source contribution actually means for most people, since it's usually done via fork + PR rather than owning a popular repo.

I hit this scoring my own resume: I have done several OS contributions, via a personal fork. The scorer gave me 5/35 on Open Source with "no contributions to other projects" as the evidence. Two reasons:

1. The fork itself gets filtered out by if repo.get("fork") and repo.get("forks_count", 0) < 5: continue — a personal contribution fork will basically always have 0 forks of its own.
2. Even without that filter, the tool only checks contributors on repos I own — never PRs I have made elsewhere.

Fix

• github.py: new fetch_external_pr_contributions(username), using the Search API (author:{username} type:pr is:merged) to find merged PRs, filtered to repos owned by someone else. Added to fetch_and_display_github_info() as external_contributions.
• transform.py: renders external_contributions into the === GITHUB DATA === block so the evaluator actually sees it.
• roles/software_engineering_intern/criteria.jinja: treat this as the primary open-source signal, and only fall back to the old "self_project-only → cap at 10" rule when there's nothing here.

Verification

Ran python score.py resume/sample.pdf --role software_engineering_intern against my own GitHub profile, before and after:

• Before: Open Source 5/35, evidence only referenced owned repos.
• After: Open Source 25/35, evidence: "N merged PRs across M repositories".

Cross-checked the merged-PR count against the GitHub Search API directly. black github.py transform.py --check passes.

Note

Only counts merged PRs (is:merged) — open/unreviewed PRs aren't counted, on purpose.