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/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "agcanvas-mcp"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+description = "MCP server bridge for agcanvas — exposes canvas tools to Claude Code, OpenCode, and Codex"
+
+[[bin]]
+name = "agcanvas-mcp"
+path = "src/main.rs"
+
+[dependencies]
+rmcp = { version = "0.14", features = ["server", "macros", "transport-io"] }
+tokio = { version = "1.0", features = ["rt-multi-thread", "macros", "io-std", "sync"] }
+tokio-tungstenite = "0.24"
+futures-util = "0.3"
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+schemars = "1.0"
+anyhow = "1.0"
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+clap = { version = "4.0", features = ["derive"] }