[FEATURE]: Automated Health Scorecard & Risk Advisor Dashboard

### Feature and its Use Cases

### What is the feature?
An **Automated Health Scorecard & Risk Advisor** that evaluates an entire GitHub organization and its individual repositories against key open-source sustainability indicators (Bus Factor, Activity Freshness, Community Governance files, and Stale PR/Issue accumulation). It synthesizes existing metrics into an organization-wide **Health Grade (A–F)** and provides maintainers with actionable **Risk Alerts & Remediation Advice**.

### How would users benefit from it?
Organization maintainers, community admins, and GSoC mentors can quickly audit org health at a glance without inspecting individual repos manually. It answers critical maintenance questions:
1. Which repositories are at high risk due to single-maintainer dependency (Bus Factor = 1)?
2. Which active repositories lack essential community standards (`CONTRIBUTING.md`, `LICENSE`, `CODE_OF_CONDUCT`)?
3. Which repos have declining activity or accumulating unreviewed PRs?

### What scenarios would this feature address?
- Preparing open-source organizations for major community events or GSoC applications.
- Identifying single-point-of-failure risks before key maintainers step down or go inactive.
- Tracking health score improvements over time across all repositories.

### Key Capabilities & Components
1. **Organization Health Summary Card**: Aggregate Health Grade (A+, A, B, C, D, F) calculated from normalized repository scores.
2. **Automated Risk Advisor Panel**: Contextual recommendation cards powered by rule engines (e.g. Critical Bus Factor warnings, missing documentation alerts, PR bottleneck flags).
3. **Interactive Health Radar & Filter Table**: Filter repos by risk tier (`High Risk`, `Medium Risk`, `Healthy`).

### Additional Context

### Technical Implementation Guidance
- **Data Services**: Build upon existing calculation functions in `src/services/analytics.js`:
- `computeHealthScore(repo, contributorCount)`
- `computeBusFactor(contributors)`
- `computeActivityClassification(repo)`
- **UI Component Target**: Integrate within `src/pages/GovernancePage.jsx` or as a standalone sub-tab.

### UI Mockup Concept
```
+-----------------------------------------------------------------------+
| 🏥 Org Health Scorecard: 84/100 (Grade: A) |
| [ 2 Critical Risks ] [ 4 Dormant Repos ] [ 12 Healthy Repos ] |
+-----------------------------------------------------------------------+
| 💡 Automated Risk Recommendations |
| • 🔴 High Risk: 'OrgExplorer' bus factor is 1. Invite 1 co-maintainer.|
| • 🟡 Missing Docs: 'repo-b' is missing CONTRIBUTING.md guidelines. |
+-----------------------------------------------------------------------+
```

### 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

Start by reading the existing calculation functions in src/services/analytics.js: computeHealthScore, computeBusFactor, and computeActivityClassification. Then inspect src/pages/GovernancePage.jsx to determine how the scorecard or sub-tab fits the current dashboard. Done means an organization-wide grade, risk recommendations, and a filterable repository health view cover the listed bus-factor, activity, governance-file, and stale-work indicators.

索引モデルが issue の本文から書いたものです。