feat: add study progress dashboard with subject-wise tracking

[Apekshaa007]

Description

Implemented a Study Progress Dashboard that provides users with visual insights into their study plan completion.

Features Added

• Overall study progress percentage
• Completed and pending task counts
• Subject-wise completion percentages
• Visual progress bars for each subject
• Automatic updates when task status changes
• Excludes archived tasks from progress calculations

Implementation Details

• Added generateProgressDashboard() function
• Connected dashboard updates using store.subscribe()
• Calculated progress using completed tasks divided by total active tasks
• Added responsive UI styling for progress bars and subject sections

Closes #240