Send Google Chat messages via webhook with text, rich cards, and threaded replies.

• Supports text messages with Google Chat formatting (*bold*, _italic_, `code`, <url|text> links), rich card messages (cardsV2) with headers, sections, and widgets, and threaded conversations using threadKey
• Includes five widget types: text paragraphs, decorated text (label + value with icons), button lists, images, and dividers; reference documentation for all widget types and available icons
• Provides webhook-sender.ts utility for posting to webhooks and card-builder.ts helper for constructing structured cards
• Threading requires appending &messageReplyOption=REPLY_MESSAGE_FALLBACK_TO_NEW_THREAD to webhook URL for replies; use consistent threadKey strings for related messages