EVA-119: port connection help — hover tooltips + data/resource legend (D2, D3)

[suzil]

Summary

• Add hover tooltip on each port handle showing its label and category (data ○ / resource ◇), positioned just outside the node card edge
• Enlarge port hit area: data port 12→16px, resource port 10→12px (17px diagonal bounding box)
• Add data/resource port legend at the bottom of NodePalette with matching circle/diamond icons

Test plan

• Hover a data port (circle) — tooltip shows name + "data" label to the outside of the node
• Hover a resource port (diamond) — tooltip shows name + "resource" label to the outside of the node
• NodePalette shows "Port types" legend below node list with ○ Data and ◇ Resource rows
• Port handles are visibly larger and easier to target

Closes EVA-119

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