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

This implements a comprehensive MCP Registry Browser that allows users to:
- 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, etc.)
- Install servers with a single command (/mcp-registry --install <id>)
- Preview installation configuration before applying changes
- Manage environment variable requirements

New components:
- cortex-mcp-client/src/registry/data.rs: Registry data structures
- cortex-mcp-client/src/registry/browser.rs: Interactive browser logic
- cortex-mcp-client/src/registry/installer.rs: Server installation logic
- cortex-mcp-client/src/registry/registry.json: 50+ MCP server entries

CLI command: /mcp-registry [search] [--category <cat>] [--install <id>] [--list]

Closes: AGENT_8_MCP_REGISTRY task

Author: factorydroid

Cargo.lock

@@ -23,3 +23,7 @@ anyhow = { workspace = true }
 tracing = { workspace = true }
 async-trait = { workspace = true }
 url = { workspace = true }
+dirs = { workspace = true }
+
+[dev-dependencies]
+tempfile = { workspace = true }

cortex-mcp-client/Cargo.toml

@@ -1,9 +1,17 @@
 //! MCP Client implementation for Cortex
+//!
+//! This crate provides:
+//! - MCP client for connecting to MCP servers
+//! - Transport layer implementations (stdio, HTTP)
+//! - Tool discovery and execution
+//! - Registry browser for discovering and installing MCP servers
 
 pub mod client;
 pub mod discovery;
+pub mod registry;
 pub mod transport;
 
 pub use client::McpClient;
 pub use discovery::ToolDiscovery;
+pub use registry::{McpCategory, McpInstaller, McpRegistry, McpRegistryBrowser, McpServerEntry};
 pub use transport::Transport;