fix: resolve edge persistence for image nodes and update connection styles

design(canvas): change node selected outline to Soft Sage theme

design(canvas): change node selected outline to premium soft pastel sky blue with translucent flat shadow

feat(canvas): optimize node selection, change selection color to blue, and fix connection drop empty space trigger

feat(canvas): context menu auto-connect, selected highlights, nodrag inputs

feat(canvas): localize default node labels and implement clean placeholder editing

init