feat: Slack platform + Claude-powered chat support widget

- Add Slack as customer-facing messaging platform (client, 4 MCP tools, dashboard card)
- Add /api/chat endpoint powered by Claude Haiku with SquareMCP system prompt
- Add embeddable chat-widget.js injected into all 3 sites (docs, app, www)
- Add ANTHROPIC_API_KEY, serve product/ as static files
- Update Platform type to include slack

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/chat.ts

@@ -0,0 +1,49 @@
+import Anthropic from '@anthropic-ai/sdk';
+
+const client = new Anthropic({ apiKey: process.env.ANTHROPIC_API_KEY });
+
+const SYSTEM_PROMPT = `You are a friendly and knowledgeable support assistant for SquareMCP — an AI Social Media Gateway that lets AI agents (Claude, ChatGPT, Codex CLI, etc.) post to social platforms via the Model Context Protocol (MCP).
+
+What SquareMCP does:
+- Connects AI coding assistants to social platforms: LinkedIn, TikTok, WhatsApp, Instagram, Twitter/X, Facebook, Telegram, Discord, Slack, and Email
+- Works with any MCP-compatible client: Claude Desktop, Claude Code, Cursor, Windsurf, opencode, Codex CLI
+- Provides a multi-tenant SaaS platform where each customer securely stores their own platform credentials
+- Offers a simple dashboard to connect platforms, view usage, and manage webhooks
+- Plans: Free (100 calls/month), Pro, Business
+
+How it works:
+1. Customer signs up at the SquareMCP dashboard
+2. Connects their social accounts (bot tokens, API keys)
+3. Adds the SquareMCP MCP server to their AI client config
+4. Their AI agent can now send messages, post content, read analytics — on any connected platform
+
+Common questions:
+- Pricing: Free tier available, paid plans for higher usage
+- Supported platforms: LinkedIn, TikTok, WhatsApp Business, Instagram, Twitter/X, Facebook, Telegram, Discord, Slack, Email
+- No coding required to use the dashboard; coding experience helps to get the most from MCP tool calls
+- Webhooks: customers can receive real-time events when messages arrive
+- Security: credentials are encrypted at rest, each customer's data is isolated
+
+Keep answers concise (2-4 sentences max). If you don't know something, say so and suggest emailing support@squaremcp.com. Never make up features or pricing. Speak in a warm, direct tone.`;
+
+export interface ChatMessage {
+  role: 'user' | 'assistant';
+  content: string;
+}
+
+export async function handleChat(messages: ChatMessage[]): Promise<string> {
+  if (!process.env.ANTHROPIC_API_KEY) {
+    throw new Error('ANTHROPIC_API_KEY not configured');
+  }
+
+  const response = await client.messages.create({
+    model: 'claude-haiku-4-5-20251001',
+    max_tokens: 512,
+    system: SYSTEM_PROMPT,
+    messages: messages.map(m => ({ role: m.role, content: m.content })),
+  });
+
+  const block = response.content[0];
+  if (block.type !== 'text') throw new Error('Unexpected response type');
+  return block.text;
+}