Add hover focus ring with modifier-based parent targeting

[alizme]

Summary

• Adds a hover focus ring (2px blue outline) that appears when hovering frames and text nodes on the canvas
• Holding Cmd (Mac) / Ctrl (Windows) promotes the hover target to the nearest parent frame, and clicking while held selects that parent
• Uses a single pointermove handler with DOM walking for robust hit-testing across nested and overlapping frames

Details

New file: hover-ring.svelte
Lightweight overlay component — positioned via getBoundingClientRect math, pointer-events-none, rendered below selection overlay (z-5 vs z-10).

EditorState changes:

• #deepHoveredNodeId tracks the deepest hovered node from pointer movement
• #modifierHeld tracks Cmd/Ctrl key state
• #displayedHoveredNodeId (derived) promotes to parent frame when modifier is held, falls back to deep target if no eligible parent exists
• isHoverableNode(id) — checks node is a frame or text and visible
• Hover measurements update reactively on pan/zoom changes

Canvas changes:

• pointermove walks DOM from e.target upward to find nearest [data-id] element passing isHoverableNode
• Cmd/Ctrl keydown/keyup tracked globally (before input guards) with onblur fallback
• Click with modifier held selects the promoted hover target instead of the deepest node
• Ring hidden during pan mode (spaceHeld) and when hovering the selected node

Test plan

• Hover a frame → ring appears
• Leave frame → ring disappears
• Hover text node → ring appears on text node
• Only one ring visible at a time
• Ring does not affect layout or intercept clicks
• Pan/zoom → ring follows correctly
• Hover selected frame → no duplicate ring
• Nested frames → deepest frame gets ring
• Hold Cmd/Ctrl → ring promotes to parent frame
• Release Cmd/Ctrl → ring reverts to deep target
• Cmd/Ctrl + click → selects parent frame
• Cmd-tab away → modifier state clears (no stuck state)

🤖 Generated with Claude Code