feat(tasks): add recurring task support with configurable intervals

[desireddymohithreddy0925]

Summary

Adds configurable daily, weekly, monthly, and custom day recurrence generation for tasks to eliminate manual recreation of cyclic work.

Closes #2888

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Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that changes existing behavior)
• 📝 Documentation update
• ♻️ Refactor / code cleanup (no functional change)
• ⚡ Performance improvement
• 🔒 Security fix
• 🧪 Tests only

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What Changed

• Expanded the Task schema in src/types/project-milestone.ts to support Recurrence.
• Extended the Kanban board creation form with interval drop-downs and custom days input.
• Added drop event listeners: Moving a recurring task to the "Done" column will automatically calculate the next interval offset and spawn a new task in the "To Do" column.

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How to Test

1. In the Kanban Board, click "New Task".
2. Create a task and set the recurrence drop-down to "Daily".
3. Add the task, then drag it into the "Done" column.
4. Look in the "To Do" column.

Expected result: A brand new task with the exact same properties is automatically spawned in "To Do", but its due date is advanced exactly one day forward.

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Checklist

• Linked the related issue above
• Self-reviewed my own diff
• No unnecessary console.log, debug code, or commented-out blocks
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Added or updated tests where applicable
• Updated documentation / comments if behavior changed

[github-actions]

GSSoC Label Checklist 🏷️

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