fix: offline sync conflict resolution and double-submission race conditions (#674)

[knoxiboy]

Resolves #674

Description

This PR refactors the offline sync logic to use a serialized first-in-first-out (FIFO) queue and introduces a conflict-resolution system with three strategies: Server Wins, Client Wins, and Merge. It prevents database ID conflicts and double-submission race conditions when syncing offline actions back to the Appwrite server.

What changed

• Updated syncPendingActions in src/offline-sync.js to run tasks sequentially.
• Integrated a check that fetches the server state of the record via /api/records/${id} prior to applying updates.
• Refactored src/conflict-resolver.js to implement resolveConflict supporting server-wins, client-wins, and merge strategies.
• Prompts the user using window.confirm for manual selection on critical conflicts under the merge strategy.
• Deletes items from IndexedDB only after a successful server acknowledgment.

Why

When internet connection recovers, rapid parallel uploads of offline actions can overwrite each other or create duplicate database entries, causing race conditions. Serializing writes and checking server timestamps solves this issue.

How to test

1. Run npm run test to verify structure health.
2. Go offline in the app and perform some dispatch/pickup updates.
3. Edit the same records directly on the server (simulated) to simulate a conflict.
4. Reconnect the app to online state and verify that the sync queue correctly compares timestamps, prompts the user for status discrepancies, and applies the selected strategy sequentially.

Checklist

• Tested changes locally
• No lint/syntax errors introduced
• Matches all issue criteria

Files Affected

• src/offline-sync.js
• src/conflict-resolver.js

[knoxiboy]

@Shruti070107 Please review this pr and merge it

[knoxiboy]

@Shruti070107 Please review this pr and merge it