feat(protocols): MCP tool adapter + Tauri commands + initialize bug fix

S6 MCP Protocol:
- Fix McpTransport::initialize() — store actual server capabilities instead
  of discarding them and storing empty ServerCapabilities::default()
- Add send_notification() method to McpTransport for JSON-RPC notifications
- Send notifications/initialized after MCP handshake (spec requirement)
- Add McpToolAdapter: bridges MCP server tools into the tool execution path
- Add McpServiceManager: lifecycle management for MCP server connections
- Add 4 Tauri commands: mcp_start_service, mcp_stop_service,
  mcp_list_services, mcp_call_tool
- Register zclaw-protocols dependency in desktop Cargo.toml

New files:
- crates/zclaw-protocols/src/mcp_tool_adapter.rs (153 lines)
- desktop/src-tauri/src/kernel_commands/mcp.rs (145 lines)

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

crates/zclaw-protocols/src/lib.rs

@@ -7,12 +7,14 @@
 
 mod mcp;
 mod mcp_types;
+mod mcp_tool_adapter;
 mod mcp_transport;
 #[cfg(feature = "a2a")]
 mod a2a;
 
 pub use mcp::*;
 pub use mcp_types::*;
+pub use mcp_tool_adapter::*;
 pub use mcp_transport::*;
 #[cfg(feature = "a2a")]
 pub use a2a::*;