[FEATURE]: Add a Repository Health & Risk Scorecard

### Feature and its Use Cases

Introduce a Repository Health & Risk Scorecard in AOSSIE Org Explorer to provide a clear, actionable overview of the health and maintenance risks of repositories within an organization.

The feature would calculate an Overall Health Score (0–100) for each repository using five weighted pillars:

Bus Factor — identifies single-maintainer or low-maintainer risks.
Governance Compliance — checks repository governance indicators such as license, README, CONTRIBUTING.md, and SECURITY.md.
Activity Freshness — evaluates how recently the repository has been updated.
Issue Responsiveness — measures the proportion of stale open issues and other responsiveness indicators.
PR Resolution Rate — evaluates how effectively pull requests are being resolved/merged.

The Governance section would include a new Health Scorecard tab where repositories can be viewed as individual scorecards.

Each scorecard could display:

Overall health score with a visual radial gauge
Pillar-by-pillar health breakdown
Risk/severity indicators
Automatically generated recommendations
Repository search and pagination
Organization-level summary such as average health and repositories at risk

This would help maintainers and organization administrators quickly identify repositories that need attention instead of having to inspect multiple governance metrics separately.

### Additional Context

The proposed implementation keeps the scoring logic separate from the UI as a pure, testable function and reuses existing repository, contributor, issue, PR, and health-related data wherever possible.

The proposed data flow is:

GitHub API → existing repository/issues/PR data → health scoring engine → repoScorecards → Governance UI

For CONTRIBUTING.md and SECURITY.md detection, the GitHub Contents API could optionally be used behind PAT authentication to avoid excessive unauthenticated API requests.

The scorecards would be sorted from worst to best so that repositories requiring attention are surfaced first.

I would also add unit tests covering each scoring pillar, overall score calculation, and recommendation edge cases.

The main goal is to turn the existing governance information into an actionable repository health overview rather than just a collection of audit metrics.

### Code of Conduct

- [x] I have joined the [Discord server](https://discord.gg/hjUhu33uAn) and will post updates there
- [x] I have searched existing issues to avoid duplicates

No repository files or entry points are named. Start by locating the existing Governance UI and the repository, contributor, issue, PR, and health-related data it uses, then trace how that data reaches the UI. Done means a separate, testable scoring function, scorecard display and sorting, organization summaries, recommendations, and unit tests for each pillar and edge cases.

索引モデルが issue の本文から書いたものです。