feat: selectable marker shapes per edge endpoint

Replace the on/off arrowhead toggle with a per-end shape picker. Each end
(start/end) independently selects: none, arrow, arrow-open, circle, diamond,
or square. Markers still recolor live from the resolved stroke color.

Frontend:
- MarkerShape type + edgeMarkers util (normalizeMarker, MARKER_GEOMETRY);
  legacy boolean coerces to 'arrow' on read.
- Per-shape <marker> inner geometry; symmetric shapes use fixed orient.
- MarkerShapePicker reused in EdgeModal and CustomStyleModal.
- Serializer normalizes to shape strings.

Backend:
- Edge marker columns Boolean -> String (default 'none'); TEXT migration.
- normalize_marker() + validators coerce legacy bool / unknown values.

ha-relevant: yes

frontend/src/components/modals/__tests__/CustomStyleModal.test.tsx

@@ -124,26 +124,26 @@ describe('CustomStyleModal', () => {
     expect(markUnsaved).not.toHaveBeenCalled()
   })
 
-  it('edge editor exposes Start/End arrow toggles defaulting off', () => {
+  it('edge editor exposes Start/End marker pickers defaulting to none', () => {
     render(<CustomStyleModal open onClose={vi.fn()} />)
     fireEvent.click(screen.getByRole('button', { name: 'Edges' }))
     fireEvent.click(screen.getByRole('button', { name: /Ethernet/ }))
-    const startBtn = screen.getByRole('button', { name: 'Start' })
-    const endBtn = screen.getByRole('button', { name: 'End' })
-    expect(startBtn.getAttribute('aria-pressed')).toBe('false')
-    expect(endBtn.getAttribute('aria-pressed')).toBe('false')
+    const startNone = screen.getByRole('button', { name: 'Start marker none' })
+    const endNone = screen.getByRole('button', { name: 'End marker none' })
+    expect(startNone.getAttribute('aria-pressed')).toBe('true')
+    expect(endNone.getAttribute('aria-pressed')).toBe('true')
   })
 
-  it('toggling End arrow feeds arrowEnd to applyTypeEdgeStyle', () => {
+  it('picking an End shape feeds arrowEnd to applyTypeEdgeStyle', () => {
     const applyTypeEdgeStyle = vi.fn()
     useCanvasStore.setState({ applyTypeEdgeStyle })
     render(<CustomStyleModal open onClose={vi.fn()} />)
     fireEvent.click(screen.getByRole('button', { name: 'Edges' }))
     fireEvent.click(screen.getByRole('button', { name: /Ethernet/ }))
-    fireEvent.click(screen.getByRole('button', { name: 'End' }))
+    fireEvent.click(screen.getByRole('button', { name: 'End marker diamond' }))
     fireEvent.click(screen.getByRole('button', { name: /Apply to existing Ethernet/ }))
-    expect(applyTypeEdgeStyle.mock.calls[0][1].arrowEnd).toBe(true)
-    expect(applyTypeEdgeStyle.mock.calls[0][1].arrowStart).toBe(false)
+    expect(applyTypeEdgeStyle.mock.calls[0][1].arrowEnd).toBe('diamond')
+    expect(applyTypeEdgeStyle.mock.calls[0][1].arrowStart).toBe('none')
   })
 
   it('editing path style updates the edge draft', () => {

frontend/src/components/modals/__tests__/EdgeModal.test.tsx

@@ -165,39 +165,56 @@ describe('EdgeModal', () => {
     expect(onSubmit.mock.calls[0][0].animated).toBe('basic')
   })
 
-  // ── Arrow markers ─────────────────────────────────────────────────────────
+  // ── Endpoint markers ──────────────────────────────────────────────────────
 
-  it('arrows default to off', () => {
+  it('endpoints default to none', () => {
     const onSubmit = vi.fn()
     render(<EdgeModal open onClose={vi.fn()} onSubmit={onSubmit} />)
     fireEvent.click(screen.getByRole('button', { name: 'Connect' }))
-    expect(onSubmit.mock.calls[0][0].marker_start).toBe(false)
-    expect(onSubmit.mock.calls[0][0].marker_end).toBe(false)
+    expect(onSubmit.mock.calls[0][0].marker_start).toBe('none')
+    expect(onSubmit.mock.calls[0][0].marker_end).toBe('none')
   })
 
-  it('toggling End arrow sends marker_end: true', () => {
+  it('picking an End arrow sends marker_end: "arrow"', () => {
     const onSubmit = vi.fn()
     render(<EdgeModal open onClose={vi.fn()} onSubmit={onSubmit} />)
-    fireEvent.click(screen.getByRole('button', { name: /Arrow End/ }))
+    fireEvent.click(screen.getByRole('button', { name: 'End marker arrow' }))
     fireEvent.click(screen.getByRole('button', { name: 'Connect' }))
-    expect(onSubmit.mock.calls[0][0].marker_end).toBe(true)
-    expect(onSubmit.mock.calls[0][0].marker_start).toBe(false)
+    expect(onSubmit.mock.calls[0][0].marker_end).toBe('arrow')
+    expect(onSubmit.mock.calls[0][0].marker_start).toBe('none')
   })
 
-  it('toggling Start arrow sends marker_start: true', () => {
+  it('picking a Start circle sends marker_start: "circle"', () => {
     const onSubmit = vi.fn()
     render(<EdgeModal open onClose={vi.fn()} onSubmit={onSubmit} />)
-    fireEvent.click(screen.getByRole('button', { name: /Arrow Start/ }))
+    fireEvent.click(screen.getByRole('button', { name: 'Start marker circle' }))
     fireEvent.click(screen.getByRole('button', { name: 'Connect' }))
-    expect(onSubmit.mock.calls[0][0].marker_start).toBe(true)
+    expect(onSubmit.mock.calls[0][0].marker_start).toBe('circle')
   })
 
-  it('pre-fills arrows from initial', () => {
+  it('allows a different shape on each end', () => {
     const onSubmit = vi.fn()
-    render(<EdgeModal open onClose={vi.fn()} onSubmit={onSubmit} initial={{ marker_start: true, marker_end: true }} />)
+    render(<EdgeModal open onClose={vi.fn()} onSubmit={onSubmit} />)
+    fireEvent.click(screen.getByRole('button', { name: 'Start marker diamond' }))
+    fireEvent.click(screen.getByRole('button', { name: 'End marker square' }))
     fireEvent.click(screen.getByRole('button', { name: 'Connect' }))
-    expect(onSubmit.mock.calls[0][0].marker_start).toBe(true)
-    expect(onSubmit.mock.calls[0][0].marker_end).toBe(true)
+    expect(onSubmit.mock.calls[0][0].marker_start).toBe('diamond')
+    expect(onSubmit.mock.calls[0][0].marker_end).toBe('square')
+  })
+
+  it('pre-fills endpoint shapes from initial', () => {
+    const onSubmit = vi.fn()
+    render(<EdgeModal open onClose={vi.fn()} onSubmit={onSubmit} initial={{ marker_start: 'diamond', marker_end: 'arrow-open' }} />)
+    fireEvent.click(screen.getByRole('button', { name: 'Connect' }))
+    expect(onSubmit.mock.calls[0][0].marker_start).toBe('diamond')
+    expect(onSubmit.mock.calls[0][0].marker_end).toBe('arrow-open')
+  })
+
+  it('coerces a legacy boolean initial marker to "arrow"', () => {
+    const onSubmit = vi.fn()
+    render(<EdgeModal open onClose={vi.fn()} onSubmit={onSubmit} initial={{ marker_end: true }} />)
+    fireEvent.click(screen.getByRole('button', { name: 'Connect' }))
+    expect(onSubmit.mock.calls[0][0].marker_end).toBe('arrow')
   })
 
   it('selecting None after Snake omits animated from payload', () => {