docs: update README and AGENTS.md with boolean ops, undo tree, new architecture

- Document boolean shape operations feature and boolean_op MCP tool
- Document visual undo tree with Cmd+H shortcut
- Add BooleanOp to WebSocket protocol examples
- Update architecture tree with history.rs, boolean.rs modules
- Add i_overlay and earcutr to dependency table
- Update roadmap: mark boolean ops and undo tree as complete

AGENTS.md

@@ -11,6 +11,7 @@ Guidelines for AI agents working in this Rust codebase.
 - WebSocket: tokio-tungstenite
 - Serialization: serde/serde_json
 - Error handling: anyhow/thiserror
+- Boolean ops: i_overlay, triangulation: earcutr
 - Logging: tracing
 
 ## Build/Lint/Test Commands
@@ -37,8 +38,19 @@ cargo doc --open               # Generate and open docs
 src/
 ├── main.rs              # Entry point, window setup
 ├── app.rs               # Main app state, UI (eframe::App impl)
+├── session.rs           # Session/tab state with history integration
+├── history.rs           # Undo tree: branching history, snapshots, checkout, fork
+├── persistence.rs       # Workspace save/load
+├── command_palette.rs   # Cmd+K fuzzy command palette
 ├── element_tree.rs      # ElementTree, Element, ElementKind types
 ├── clipboard.rs         # System clipboard integration
+├── mermaid.rs           # Mermaid -> SVG rendering
+├── drawing/
+│   ├── element.rs       # DrawingElement, Shape (incl. Path), ShapeStyle, hit testing
+│   ├── boolean.rs       # Boolean shape ops (union, intersection, difference, xor)
+│   ├── tool.rs          # Tool enum, DragState, ResizeHandle
+│   ├── render.rs        # Shape rendering via egui Painter + triangulation
+│   └── mod.rs           # Re-exports
 ├── canvas/
 │   ├── state.rs         # Pan/zoom transformation state
 │   └── interaction.rs   # Mouse/keyboard input handling
@@ -46,7 +58,7 @@ src/
 │   ├── parser.rs        # SVG -> ElementTree conversion
 │   └── renderer.rs      # SVG -> pixels (resvg/tiny-skia)
 └── agent/
-    ├── protocol.rs      # JSON message types
+    ├── protocol.rs      # JSON message types (incl. BooleanOp)
     └── server.rs        # WebSocket server (ws://127.0.0.1:9876)
 ```
 
@@ -163,6 +175,7 @@ WebSocket server on `ws://127.0.0.1:9876`:
 {"type": "GetElementById", "id": "button-1"}
 {"type": "Describe"}
 {"type": "GenerateCode", "target": "react", "element_id": null}
+{"type": "BooleanOp", "operation": "union", "element_ids": ["id1", "id2"], "consume_sources": true}
 
 // Response
 {"type": "Tree", "tree": {...}}