fix(user_status): make setUserStatus() idempotent for concurrent duplicate requests

[miaulalala]

Summary

When two automated events of the same type fire simultaneously (e.g. a calendar webhook is delivered twice, or two Talk clients both trigger a call status at the same time), both requests race through setUserStatus().

The first request succeeds: it creates a backup of the user's previous status and sets the new automated status. The second request finds the backup slot already occupied (unique constraint on user_id), so backupCurrentStatus() returns false. Previously this caused setUserStatus() to return null, which the caller interpreted as a failure even though the desired status was already correctly set by the first request.

Fix: after backupCurrentStatus() returns false, re-read the current active status row. If it already carries the same messageId that we were trying to set, the operation is effectively complete — return the existing status instead of null. If it carries a different messageId (a higher-priority automated status is active), we still return null to abort as before.

This also covers the meeting-with-call scenario: if a calendar BUSY status is active and a Talk call starts, the call correctly overrides it via the priority shortcut path. If the calendar fires a duplicate webhook while the call is already active, the re-read finds MESSAGE_CALL ≠ MESSAGE_CALENDAR_BUSY and correctly aborts rather than overriding the ongoing call.

AI-Assisted-By: Claude Sonnet 4.6 noreply@anthropic.com

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI