[Feat] Create a Weekly Summary of Completed Tasks

**Is your feature request related to a problem? Please describe.**
Currently, there is no way for users to quickly review the tasks they’ve completed over the course of the week. Without a weekly summary, users may find it difficult to track their progress and accomplishments, which can affect their motivation and productivity.

**Describe the solution you'd like**
Generate a weekly summary of tasks that were completed within the past week.
Display the list of completed tasks, showing task titles, completion dates, and any other relevant details (e.g., priority, due date, etc.).
Include a clear section on the home screen or in a separate “Summary” page that aggregates completed tasks by week, making it easy for users to review their weekly progress.
Optionally, show statistics such as the total number of tasks completed or a breakdown of task priorities.

**Additional context**
Mockups will be added by our design team

Start by reviewing the existing Flutter task model and home-screen structure to understand how completed tasks and dates are represented. The work is done when users can view a weekly summary listing completed task titles and completion dates, with any agreed priority or statistics details, after the design mockups are available.

Written by the indexing model from the issue text.