Remove debug printf statements from BluetoothDeviceManager

[Copilot]

Addresses feedback on #35 to remove debug code before merge.

Changes

• Removed 11 debug printf statements from BluetoothDeviceManager.cpp - all statements with *** _DEBUG: prefix
• Added .gitignore to exclude build artifacts (build/, CMakeCache.txt, compiled objects)

Proper logging via LOGERR() macro remains intact for error conditions.

// Before
if (pPersistentStore == nullptr) {
    printf("*** _DEBUG: BluetoothDeviceManager::updateBluetoothDeviceInfoCache: Failed to get PersistentStore interface\n");
    LOGERR("Failed to get PersistentStore interface\n");
    return Core::ERROR_GENERAL;
}

// After
if (pPersistentStore == nullptr) {
    LOGERR("Failed to get PersistentStore interface\n");
    return Core::ERROR_GENERAL;
}

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