When capabilities is configured as an object (e.g., { inlineButtons: "dm" })
instead of a string array, normalizeCapabilities() would crash with
"capabilities.map is not a function".
This can occur when using the new Telegram inline buttons scoping feature:
channels.telegram.capabilities.inlineButtons = "dm"
The fix adds an Array.isArray() guard to return undefined for non-array
capabilities, allowing channel-specific handlers (like
resolveTelegramInlineButtonsScope) to process the object format separately.
Fixes crash when using object-format TelegramCapabilitiesConfig.
