- Add resolveNodeColors() utility merging type defaults with per-node overrides
- Default colors per node type (cyan=isp/router/lxc/ap, green=switch/nas,
purple=server/vm, orange=proxmox, amber=iot, gray=generic)
- Remove glowColor prop from BaseNode — colors now come from node data
- ProxmoxGroupNode uses resolveNodeColors for group border/header/icon
- NodeModal: Appearance section with 3 color swatches (border, background, icon)
— click swatch to open native color picker; Reset to defaults button
- custom_colors persisted as JSON in DB (backend model + schemas + migration)
- 7 new unit tests for resolveNodeColors covering all node types + partial overrides