fix(FirestoreDb): correct getLatestAlarm else branch to use current minute without offset

[dorodb-web22]

Description

Fixes #880
As noted in the issue, the else branch of getLatestAlarm inside firestore_provider.dart was an identical copy of the if branch (both added + 1 to the current minute). This caused wantNextAlarm = false to behave exactly like wantNextAlarm = true.

Proposed Changes

Removed the + 1 from the else branch. This logic now correctly matches the Isar provider's implementation of the same method.

Screenshots

N/A

Checklist

• Tests have been added or updated to cover the changes
• Documentation has been updated to reflect the changes
• Code follows the established coding style guidelines
• All tests are passing