feat(mcp): Add MCP Registry Browser for discovering and installing MCP servers

[echobt]

Summary

This PR implements a comprehensive MCP Registry Browser that allows users to discover and install MCP servers from an embedded registry of 50+ pre-configured servers.

Features

MCP Registry Browser CLI

• Command: /mcp-registry [search] [--category <cat>] [--install <id>] [--list]
• Browse 50+ pre-configured MCP servers from an embedded registry
• Search servers by name, description, ID, and tags
• Filter servers by category (Development, Database, Security, Productivity, Communication, Cloud, AI, Web, Files, Other)
• Install servers with a single command
• Preview installation configuration before applying changes

Server Categories

• 🔧 Development: GitHub, GitLab, Playwright, Sentry, Docker, Honeycomb
• 🗃️ Database: PostgreSQL, MySQL, MongoDB, Redis, SQLite, Supabase, Neon, Prisma
• 🔒 Security: Snyk, Semgrep
• 📋 Productivity: Linear, Jira, Notion, Todoist, Google Calendar
• 💬 Communication: Slack, Discord, Email, Twilio
• ☁️ Cloud: AWS, Azure, GCP, Vercel, Cloudflare, Kubernetes, Stripe
• 🤖 AI: Memory, Sequential Thinking, OpenAI, Anthropic, Braintrust
• 🌐 Web: Brave Search, Google Search, Fetch, Puppeteer, Google Maps
• 📁 Files: Filesystem, Google Drive, Dropbox

Technical Implementation

• cortex-mcp-client/src/registry/data.rs: Core registry data structures
• cortex-mcp-client/src/registry/browser.rs: Interactive browser with search and filtering
• cortex-mcp-client/src/registry/installer.rs: Server installation with environment validation
• cortex-mcp-client/src/registry/registry.json: 50+ MCP server entries with metadata

CLI Examples

# Open interactive registry browser
/mcp-registry

# Search for database servers
/mcp-registry database

# Filter by category
/mcp-registry --category db

# Install a server
/mcp-registry --install postgres

# List all servers
/mcp-registry --list

Testing

• All unit tests pass for registry data structures, browser logic, and installer
• cargo check passes for cortex-mcp-client and cortex-tui
• cargo fmt applied

Related

Implements AGENT_8_MCP_REGISTRY task from orchestration