feat: add visual builder + workspace mode to Burr UI

[andreahlert]

Building on #667 (Graph Builder by @skrawcz), this adds a workspace mode and significantly enhanced builder that turns Burr's UI into a development environment.

What's new

Visual Builder (enhanced)

• 9 node types: Action, Input, Result, LLM Call, API Call, Code, Streaming, Loop, Router
• Each type has specialized property editors (LLM: provider/model, API: url/method, Code: inline editor, Router: branch conditions)
• Inline + button on edges (Activepieces-style) with searchable type picker
• Recursive layout algorithm (replaces dagre) supporting loop arcs and router fan-out/fan-in
• Node type picker with search bar and categories (I/O, Logic, Integrations)

Monaco Editor (split view)

• Builder canvas on the left, VS Code-style editor on the right
• Multi-file code generation: actions.py, app.py, run.py, requirements.txt
• File explorer sidebar with tabs (open/close files)
• Bidirectional sync: edit code and the graph updates, edit graph and the code updates
• Full Ctrl+C/V/Z support in both canvas and editor

Project save/load

• File menu (New, Save, Open, Download .py)
• Projects persisted server-side in ~/.burr/builder_projects/
• Ctrl+S to save

Workspace integration

• Backend workspace router with file browsing, code viewing, and script execution (SSE streaming)
• Link workspace directories to projects
• Path traversal protection with workspace validation

Other improvements

• Undo/redo with 50-state history
• Keyboard shortcuts (Delete to remove nodes, Ctrl+C/V to copy/paste nodes)
• Code generation includes proper imports, sanitized identifiers, and with_tracker()

Screenshots

Builder with nodes and generated code

Node editor with LLM Call configuration

Searchable node type picker

Technical details

Backend (Python)

• burr/tracking/server/workspace.py: new APIRouter with endpoints for file tree, file content, script execution (SSE), process management, workspace links, and builder project persistence
• Modified run.py to mount workspace router, schema.py to add supports_workspace

Frontend (~6,700 new lines)

• utils/: builderTypes, codeGenerator (9 node types + multi-file), codeParser (bidirectional sync), flowLayout (recursive layout), treeUtils (immutable tree ops), stateFlow
• hooks/useBuilderState.ts: tree-based state with undo/redo, keyboard shortcuts, save/load
• builder/: BuilderView (split layout), BuilderGraph (ReactFlow with custom node/edge types), NodeEditor, NodeTypePicker (portal-based), 4 node components, 5 edge components with inline + buttons
• workspace/: FileExplorer, CodeViewer, RunTerminal, WorkspaceSelector
• project/: ProjectWorkspaceView, ActivityBar, SidePanel, TabBar, TrackingSidePanel

Dependencies added

• @monaco-editor/react (MIT)
• @tanstack/react-query (MIT)
• @xyflow/react (MIT)
• react-joyride (MIT)

All MIT license, ASF Category A compatible.

How I tested

• npx tsc --noEmit zero errors
• Backend endpoints tested with curl
• Manual E2E: create flow, add nodes via toolbar and inline +, edit properties, see code update, save/load projects

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal
• Code passed the pre-commit check
• New functions are documented
• Placeholder code is flagged / future TODOs are captured in comments