fix: add circular dependency detection for tasks

[Vasist10]

Description

Added cycle detection to prevent task dependency loops (e.g., Task A → Task B → Task A).

• DFS algorithm with O(V + E) complexity for optimal cycle detection

• Validates dependencies during add/edit/modify operations

• Fixes: Circular dependency in task dependencies #308

Checklist

• Ran npx prettier --write . (for formatting)
• Ran gofmt -w . (for Go backend)
• Ran npm test (for JS/TS testing)
• Added unit tests, if applicable
• Verified all tests pass
• Updated documentation, if needed

Additional Notes

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[Vasist10]

the latest 3 commits fix:

• Improve the toast message to make to more clearer from a generic message
• Fix an issue where a task involved in a circular dependency still appeared in the UI even after the backend rejected the update, until a manual sync was triggered.
  ex:
  In this below image the task 'panic' forms a circular dependency with task 'panib' and task 'pania'.....but still even after the backend rejects the dependency the task 'panic' is appearing in the frontend(until sync was applied).

this ui buggy behavior is fixed now

[Vasist10]

@its-me-abhishek i have added the self review and fixed the ui buggy behavior.