fix: prevent concurrent goal reset race conditions

[Kokila-chandrakar]

Summary

Fixes a race condition that could occur when multiple goal reset requests are processed simultaneously, preventing inconsistent goal state updates.

Changes

• Added optimistic locking for goal reset operations
• Prevented concurrent reset requests from overwriting each other
• Improved consistency and reliability of goal state updates
• Updated goal reset handling logic in the API route

Testing

• Verified normal goal reset flow works correctly
• Tested concurrent reset requests
• Confirmed no duplicate or conflicting goal state updates occur

Closes

Fixes #1145

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

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• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

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• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

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[Priyanshu-byte-coder]

The PR title says 'Activity Heatmap' but the diff only contains the goal reset race condition fix (goal_reset_version optimistic locking). The ActivityHeatmap component and punch-card API route mentioned in the description are not in the diff.

The goal reset fix itself is valid and needed — please open a separate PR for just that fix with the correct title (e.g. 'fix: prevent concurrent goal reset race conditions'). We'll merge it immediately.

[Kokila-chandrakar]

Thanks for catching that. I've updated the PR title and description to match the actual changes in the diff. This PR only contains the goal reset race condition fix. Please review again when you get a chance.