🧪 [testing improvement] Add unit tests for Sync Server endpoints

[FrogletApps]

🧪 Add unit tests for Sync Server endpoints (/api/sync/pull and /api/sync/push)

🎯 What: The testing gap for sync server endpoints in server/src/core/app.ts addressed using Node's native test runner and Hono's app.request().

📊 Coverage:

• GET /api/sync/pull:
  • Returns 400 error when sku query parameter is missing.
  • Returns empty array and version 0 when no notes exist.
  • Filters incident notes based on since version parameter and correctly calculates latestVersion.
• POST /api/sync/push:
  • Returns 400 error when sku parameter is missing in payload.
  • Returns 400 error when changes is not an array.
  • Successfully applies note changes, returns latestVersion and appliedCount, and persists changes in storage.

✨ Result: Enhanced sync server test coverage and reliability with fast, zero-dependency unit tests running via Node's native test runner.

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PR created automatically by Jules for task 4337540522757209394 started by @FrogletApps

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