Add custom node renderers for each block type #10

Summary

Currently all blocks render as generic React Flow default nodes. Each block type (Condition, Transfer, Storage, Event, Auth) should have a distinct visual style with an icon, colour-coded header, and type label to make the canvas easier to read at a glance.

Tasks

• Create src/components/editor/nodes/ directory with one file per block type: ConditionNode.tsx, TransferNode.tsx, StorageNode.tsx, EventNode.tsx, AuthNode.tsx
• Each node component receives data props and renders a styled card with a colour-coded header and icon
• Register all custom node types in the nodeTypes prop of <ReactFlow>
• Assign the correct type when creating nodes from the toolbar drag-drop

Acceptance Criteria

• Each block type renders with a visually distinct colour and icon
• Node labels and config values are displayed inside the card
• Source and target handles are present and connectable
• Custom nodes are accessible (sufficient colour contrast, aria labels)