feat: add circular dependency detection

[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]

@its-me-abhishek The previous PR had some merge/commit history noise, so I opened this PR.

[its-me-abhishek]

@Vasist10 I had added a review in #323, kindly ACK that here wrt this PR

[Vasist10]

@its-me-abhishek yes , i have made the change wrt to your review