Dragging a guide, or moving one, now snaps to nearby layer edges and centres on the guide's own axis: within 5 screen pixels, gated by Snap to Objects and suspended with Cmd/Ctrl. Page guides see the page's top-level layers; frame guides see the frame's box, its layout grids and every visible layer inside it, in the frame's own space.
Snapping sits in the interaction path (canvas/guides.rs, not guide.add/guide.move) so the commands stay deterministic for the control channel and MCP. Tests: guide_snap_tests.rs in the engine and ui-egui crates; docs/ui-parity.md updated.
Signed-off-by: Ahmed Mahmoud <ahmedmhmouad41@gmail.com>