fix(backend): update last_synced_at when data arrives via webhook

[bartmichalak]

Description

• Garmin webhook endpoints (push/ping) processed and saved incoming data correctly but never updated last_synced_at on the user connection
• Added tracking of user IDs that successfully received data during webhook processing
• After commit, last_synced_at is now updated for all affected connections

Checklist

General

• My code follows the project's code style
• I have performed a self-review of my code
• I have added tests that prove my fix/feature works (if applicable)
• New and existing tests pass locally

Backend Changes

You have to be in backend directory to make it work:

• uv run pre-commit run --all-files passes

Frontend Changes

• pnpm run lint passes
• pnpm run format:check passes
• pnpm run build succeeds

Testing Instructions

Steps to test:
1.
2.
3.

Expected behavior:

Screenshots

Additional Notes

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/update-last-synced-at-when-data-are-updated-via-garmin-webhooks

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[railway-app]

🚅 Deployed to the open-wearables-pr-590 environment in Open Wearables

Service	Status	Web	Updated (UTC)
frontend	✅ Success (View Logs)	Web	Mar 10, 2026 at 11:43 pm
celery-flower	✅ Success (View Logs)	Web	Mar 10, 2026 at 11:43 pm
celery-worker	✅ Success (View Logs)		Mar 10, 2026 at 11:43 pm
celery-beat	✅ Success (View Logs)		Mar 10, 2026 at 11:42 pm
backend	✅ Success (View Logs)	Web	Mar 10, 2026 at 11:42 pm