Team graph #16

Why

Who builds with whom shows how the community clusters, and which builders connect different teams.

In this repo today

repo_contributors holds the GitHub contributors of every repo. The API serves one hackathon, so the first version covers the indexed event. Extending the graph across events depends on multi-hackathon support (see the past hackathon backfill issue).

What to build

• An API route returning nodes (GitHub handle, project count) and edges (weight is the number of repos two builders share), limited to verified and "code only" projects. Public GitHub handles only.
• A /graph page (pages/graph.tsx, registered in App.tsx) using d3-force in a reusable component in components/charts/.
• Clicking a node opens that person's GitHub profile. Hovering an edge lists the shared repos, each linking to its project page (/project/repo:owner/name).

Acceptance criteria

• Renders 300 nodes without jank on a laptop.
• Nodes and edges contain no data beyond public handles and repo names.

See CONTRIBUTING.md for conventions.