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/__tests__/canvasSerializer.test.ts

@@ -250,6 +250,19 @@ describe('serializeEdge', () => {
     expect(result.marker_end).toBe('arrow')
   })
 
+  it('serializes line style + width multiplier', () => {
+    const edge = makeRfEdge({ data: { type: 'wifi', line_style: 'dotted', width_mult: 3 } })
+    const result = serializeEdge(edge)
+    expect(result.line_style).toBe('dotted')
+    expect(result.width_mult).toBe(3)
+  })
+
+  it('nulls line style + width multiplier when absent', () => {
+    const result = serializeEdge(makeRfEdge())
+    expect(result.line_style).toBeNull()
+    expect(result.width_mult).toBeNull()
+  })
+
   it('coerces legacy boolean markers to shape strings', () => {
     const edge = makeRfEdge({ data: { type: 'ethernet', marker_start: true, marker_end: false } })
     const result = serializeEdge(edge)

frontend/src/utils/__tests__/edgeLineStyle.test.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect } from 'vitest'
+import {
+  EDGE_LINE_STYLES,
+  EDGE_TYPE_BASE_WIDTH,
+  EDGE_TYPE_DEFAULT_LINE,
+  clampWidthMult,
+  dashArrayFor,
+} from '@/utils/edgeLineStyle'
+import { EDGE_TYPE_LABELS } from '@/types'
+
+describe('edgeLineStyle', () => {
+  it('lists the three render styles', () => {
+    expect(EDGE_LINE_STYLES).toEqual(['solid', 'dashed', 'dotted'])
+  })
+
+  it('has a base width + default line for every edge type', () => {
+    for (const t of Object.keys(EDGE_TYPE_LABELS) as (keyof typeof EDGE_TYPE_LABELS)[]) {
+      expect(EDGE_TYPE_BASE_WIDTH[t]).toBeGreaterThan(0)
+      expect(EDGE_LINE_STYLES).toContain(EDGE_TYPE_DEFAULT_LINE[t])
+    }
+  })
+
+  it('clampWidthMult keeps values within 1..4 and defaults to 1', () => {
+    expect(clampWidthMult(undefined)).toBe(1)
+    expect(clampWidthMult(NaN)).toBe(1)
+    expect(clampWidthMult(0)).toBe(1)
+    expect(clampWidthMult(2.5)).toBe(2.5)
+    expect(clampWidthMult(9)).toBe(4)
+  })
+
+  it('dashArrayFor returns undefined for solid and a pattern otherwise', () => {
+    expect(dashArrayFor('solid', 2)).toBeUndefined()
+    expect(dashArrayFor('dashed', 2)).toBe('6 4')
+    expect(dashArrayFor('dotted', 2)).toBe('2 3.6')
+  })
+
+  it('dashArrayFor scales with stroke width', () => {
+    expect(dashArrayFor('dashed', 4)).toBe('12 8')
+  })
+})