Add drawing tools, Mermaid support, and MCP server bridge

- Convert flat project to Cargo workspace (crates/agcanvas, crates/agcanvas-mcp)
- Add drawing layer: rectangles, ellipses, lines, arrows, text with select/move/resize
- Add Mermaid diagram rendering via mermaid-rs-renderer
- Add agcanvas-mcp: MCP server bridge for Claude Code, OpenCode, and Codex
- Add toolbar UI with keyboard shortcuts (V/R/E/L/A/T) and shape interaction
- Add example MCP configs for Claude Code, OpenCode, and Codex
- Update README with full feature docs, MCP setup, and updated architecture

crates/agcanvas-mcp/src/main.rs

@@ -0,0 +1,38 @@
+mod bridge;
+mod tools;
+
+use anyhow::Result;
+use clap::Parser;
+use rmcp::ServiceExt;
+use tools::AgCanvasServer;
+use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
+
+#[derive(Parser)]
+#[command(name = "agcanvas-mcp", about = "MCP server bridge for agcanvas")]
+struct Cli {
+    #[arg(long, default_value = "9876")]
+    port: u16,
+}
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::EnvFilter::new(
+            std::env::var("RUST_LOG").unwrap_or_else(|_| "agcanvas_mcp=info".into()),
+        ))
+        .with(tracing_subscriber::fmt::layer().with_writer(std::io::stderr))
+        .init();
+
+    let cli = Cli::parse();
+    let ws_url = format!("ws://127.0.0.1:{}", cli.port);
+
+    tracing::info!("Starting agcanvas MCP server, connecting to {}", ws_url);
+
+    let server = AgCanvasServer::new(ws_url);
+    let service = server.serve(rmcp::transport::stdio()).await?;
+
+    tracing::info!("MCP server running on stdio");
+    service.waiting().await?;
+
+    Ok(())
+}