fix: Add thread safety to FileProviderService sync status tracking

[Copilot]

Description

The _latestReceivedSyncStatus QHash in FileProviderService was accessed from multiple threads without synchronization: reads from Qt threads via latestReceivedSyncStatusForAccount() and writes from XPC threads via the Objective-C delegate callback in setLatestReceivedSyncStatus().

Changes

• Added QReadWriteLock to protect _latestReceivedSyncStatus access
• Read operations use QReadLocker (allows concurrent readers)
• Write operations use QWriteLocker (exclusive access)

SyncResult::Status FileProviderService::latestReceivedSyncStatusForAccount(const AccountPtr &account) const
{
    Q_ASSERT(account);
    QReadLocker locker(&_syncStatusLock);
    return _latestReceivedSyncStatus.value(account->userIdAtHostWithPort(), SyncResult::Undefined);
}

void FileProviderService::setLatestReceivedSyncStatus(const QString &userId, SyncResult::Status status)
{
    QWriteLocker locker(&_syncStatusLock);
    _latestReceivedSyncStatus.insert(userId, status);
}

QReadWriteLock chosen over QMutex for read-heavy workload optimization.

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[Copilot]

Pull request overview

This PR adds thread safety to the FileProviderService's sync status tracking mechanism, which was previously accessing a shared QHash without synchronization from multiple threads (Qt GUI threads for reads and XPC threads for writes).

Changes:

• Added QReadWriteLock member variable to protect _latestReceivedSyncStatus QHash
• Implemented read locks for concurrent read operations in latestReceivedSyncStatusForAccount()
• Implemented write locks for exclusive write operations in setLatestReceivedSyncStatus()

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/gui/macOS/fileproviderservice.h	Added QReadWriteLock member variable and necessary include
src/gui/macOS/fileproviderservice.mm	Added QReadLocker/QWriteLocker includes and lock guards to protect QHash access

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