feat: configurable edge line style + width per type and per edge

Edge render (solid/dashed/dotted) and stroke width were hardcoded per
edge type. Expose both as user settings.

- Custom Style modal (Edges): line-style buttons, 1-4x width slider,
  live preview; left-list swatch renders the actual line.
- Per-edge EdgeModal: same controls; line style follows the type preset
  live until overridden.
- Renderer applies line_style/width_mult over BASE_STYLES (width scales
  markers + animation overlays); unset keeps the type default look.
- Persist line_style/width_mult through serializer, canvas save, and the
  edges API (new nullable columns, idempotent migration).

ha-relevant: yes

frontend/src/utils/edgeLineStyle.ts

@@ -0,0 +1,55 @@
+import type { EdgeLineStyle, EdgeType } from '@/types'
+
+/** Line render styles selectable per edge type, in picker order. */
+export const EDGE_LINE_STYLES: EdgeLineStyle[] = ['solid', 'dashed', 'dotted']
+
+export const EDGE_LINE_STYLE_LABELS: Record<EdgeLineStyle, string> = {
+  solid: 'Solid',
+  dashed: 'Dashed',
+  dotted: 'Dotted',
+}
+
+/**
+ * Base stroke width (px) per edge type — the "1×" reference the width
+ * multiplier scales from. Mirrors BASE_STYLES in canvas/edges/index.tsx.
+ */
+export const EDGE_TYPE_BASE_WIDTH: Record<EdgeType, number> = {
+  ethernet: 2,
+  wifi: 1.5,
+  iot: 1.5,
+  vlan: 2.5,
+  virtual: 1,
+  cluster: 2.5,
+  fibre: 2.5,
+  electrical: 2,
+}
+
+/** Default line render style per edge type (matches the hardcoded dash presets). */
+export const EDGE_TYPE_DEFAULT_LINE: Record<EdgeType, EdgeLineStyle> = {
+  ethernet: 'solid',
+  wifi: 'dashed',
+  iot: 'dotted',
+  vlan: 'solid',
+  virtual: 'dashed',
+  cluster: 'dashed',
+  fibre: 'solid',
+  electrical: 'solid',
+}
+
+/** Multiplier is limited to 1×–4× of the type's base width. */
+export function clampWidthMult(v: number | undefined): number {
+  if (v == null || Number.isNaN(v)) return 1
+  return Math.min(4, Math.max(1, v))
+}
+
+/**
+ * SVG `stroke-dasharray` for a line style, scaled to the stroke width.
+ * `solid` returns undefined (no dashes). `dotted` pairs with a round line cap
+ * so the short segments render as dots.
+ */
+export function dashArrayFor(style: EdgeLineStyle, strokeWidth: number): string | undefined {
+  const w = Math.max(0.5, strokeWidth)
+  if (style === 'dashed') return `${w * 3} ${w * 2}`
+  if (style === 'dotted') return `${w} ${w * 1.8}`
+  return undefined
+}