[FEATURE]: Centralized Weekly Progress Tracker & Contribution Matrix

### Feature and its Use Cases

**Feature and its Use Cases**
**What is the feature?**
An interactive **"Weekly Progress Tracker"** dashboard inside OrgExplorer. It will provide a matrix grid view showing a filtered subset of contributors along with a week-by-week chronological breakdown of their development activity (PRs opened, merged, closed, and issues raised).

**How would users benefit from it?**
Currently, organization mentors and GSoC contributors manually input and verify weekly contributions in a progress spreadsheet. Automating this within OrgExplorer will:
1. Save significant administrative time for mentors and students alike.
2. Provide a single, source-of-truth dashboard that reads directly from the GitHub API.
3. Automatically compute weekly metrics without manual entry errors.

**What scenarios would this feature address?**

- Mentor Evaluations: Mentors can easily check the week-by-week performance and velocity of all contributors in a single screen.
- Student Milestone Checks: Contributors can track their weekly progress to ensure they are meeting their target timelines.
- Sprint / Coding Window Audits: Allows checking activity patterns over standard weekly sprint intervals.

### Additional Context

**Proposed UI Design & Layout**

- Filters: Select date range, start week configuration, and filter contributor lists (with an option to save filtered subsets like "GSoC 2026 Cohort").
- Matrix Grid:
- Columns: Weeks (e.g., Week 1: May 18 - May 24, Week 2: May 25 - May 31).
- Rows: Contributor usernames.
- Cells: Aggregated badges showing active counts (e.g., 3 PRs / 1 Issue).
- Details Modal: Clicking on any cell opens a modal detail pane showing the titles, status, and direct GitHub links of all PRs/Issues submitted in that specific week.

**Project References**
Addresses the open item outlined in
`FeatureWishlist.md`

### 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 with FeatureWishlist.md, then inspect OrgExplorer's existing dashboard and GitHub API entry points. Clarify the date-range and week filters, contributor subsets, matrix metrics, and detail modal behavior before implementation; done means the described weekly tracker provides linked PR and issue details from the GitHub API.

索引モデルが issue の本文から書いたものです。