feat: manage canvases with custom name and icon

Make designs (canvases) fully user-manageable: create with a chosen name
and icon, rename, change icon, and delete. Replaces the hardcoded
"New Electrical Design" button with a generic "New Canvas" flow.

- Add Design.icon column + migration that backfills legacy rows
  (electrical -> zap, others -> dashboard)
- DesignModal: name input + curated lucide icon picker (create + edit)
- Sidebar switcher gains per-canvas edit/delete; delete guards the last
  canvas and confirms
- designStore: addDesign/updateDesign/removeDesign with active reassignment
- Fix data loss on design switch: abort load when the save fails and keep
  unsaved edits; skip the save-old step when the previous canvas was deleted
- designsApi create/update carry icon; design_type kept for back-compat

Tests: backend design CRUD (icon + cascade + last-canvas guard), designStore
actions, designIcons resolver, DesignModal create/edit/validation.

ha-relevant: yes

frontend/src/components/modals/DesignModal.tsx

@@ -0,0 +1,87 @@
+import { useState } from 'react'
+import { Dialog, DialogContent, DialogHeader, DialogTitle, DialogFooter } from '@/components/ui/dialog'
+import { Button } from '@/components/ui/button'
+import { Label } from '@/components/ui/label'
+import { Input } from '@/components/ui/input'
+import { DESIGN_ICONS, DEFAULT_DESIGN_ICON } from '@/utils/designIcons'
+
+export interface DesignFormData {
+  name: string
+  icon: string
+}
+
+interface DesignModalProps {
+  open: boolean
+  onClose: () => void
+  onSubmit: (data: DesignFormData) => void
+  initial?: DesignFormData
+  title?: string
+  submitLabel?: string
+}
+
+export function DesignModal({ open, onClose, onSubmit, initial, title = 'New Canvas', submitLabel = 'Create' }: DesignModalProps) {
+  const [name, setName] = useState(initial?.name ?? '')
+  const [icon, setIcon] = useState(initial?.icon ?? DEFAULT_DESIGN_ICON)
+
+  const handleSubmit = () => {
+    const trimmed = name.trim()
+    if (!trimmed) return
+    onSubmit({ name: trimmed, icon })
+  }
+
+  return (
+    <Dialog open={open} onOpenChange={(o) => !o && onClose()}>
+      <DialogContent className="sm:max-w-md">
+        <DialogHeader>
+          <DialogTitle>{title}</DialogTitle>
+        </DialogHeader>
+
+        <div className="space-y-4 py-2">
+          <div className="space-y-1.5">
+            <Label htmlFor="design-name">Name</Label>
+            <Input
+              id="design-name"
+              value={name}
+              onChange={(e) => setName(e.target.value)}
+              onKeyDown={(e) => { if (e.key === 'Enter') handleSubmit() }}
+              placeholder="e.g. Home Network, Rack Power"
+              autoFocus
+            />
+          </div>
+
+          <div className="space-y-1.5">
+            <Label>Icon</Label>
+            <div className="grid grid-cols-8 gap-1.5">
+              {DESIGN_ICONS.map((entry) => {
+                const Icon = entry.icon
+                const selected = entry.key === icon
+                return (
+                  <button
+                    key={entry.key}
+                    type="button"
+                    aria-label={entry.label}
+                    aria-pressed={selected}
+                    title={entry.label}
+                    onClick={() => setIcon(entry.key)}
+                    className={`flex items-center justify-center aspect-square rounded-md border transition-colors cursor-pointer ${
+                      selected
+                        ? 'border-[#00d4ff] bg-[#00d4ff]/10 text-[#00d4ff]'
+                        : 'border-border text-muted-foreground hover:text-foreground hover:border-[#30363d]'
+                    }`}
+                  >
+                    <Icon size={16} />
+                  </button>
+                )
+              })}
+            </div>
+          </div>
+        </div>
+
+        <DialogFooter>
+          <Button variant="ghost" onClick={onClose}>Cancel</Button>
+          <Button onClick={handleSubmit} disabled={!name.trim()}>{submitLabel}</Button>
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  )
+}

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

@@ -0,0 +1,67 @@
+import { describe, it, expect, vi } from 'vitest'
+import { render, screen, fireEvent } from '@testing-library/react'
+import { DesignModal } from '../DesignModal'
+import { DEFAULT_DESIGN_ICON } from '@/utils/designIcons'
+
+function renderModal(props: Partial<Parameters<typeof DesignModal>[0]> = {}) {
+  const onClose = vi.fn()
+  const onSubmit = vi.fn()
+  render(<DesignModal open onClose={onClose} onSubmit={onSubmit} {...props} />)
+  return { onClose, onSubmit }
+}
+
+describe('DesignModal', () => {
+  it('creates with the typed name and default icon', () => {
+    const { onSubmit } = renderModal()
+    fireEvent.change(screen.getByLabelText('Name'), { target: { value: 'Home Network' } })
+    fireEvent.click(screen.getByRole('button', { name: 'Create' }))
+    expect(onSubmit).toHaveBeenCalledWith({ name: 'Home Network', icon: DEFAULT_DESIGN_ICON })
+  })
+
+  it('submits the selected icon', () => {
+    const { onSubmit } = renderModal()
+    fireEvent.change(screen.getByLabelText('Name'), { target: { value: 'Rack Power' } })
+    fireEvent.click(screen.getByRole('button', { name: 'Electrical' })) // zap icon's aria-label
+    fireEvent.click(screen.getByRole('button', { name: 'Create' }))
+    expect(onSubmit).toHaveBeenCalledWith({ name: 'Rack Power', icon: 'zap' })
+  })
+
+  it('trims whitespace and blocks empty names', () => {
+    const { onSubmit } = renderModal()
+    // Empty → submit disabled, no call.
+    const submit = screen.getByRole('button', { name: 'Create' })
+    expect(submit).toBeDisabled()
+
+    fireEvent.change(screen.getByLabelText('Name'), { target: { value: '  Spaced  ' } })
+    fireEvent.click(submit)
+    expect(onSubmit).toHaveBeenCalledWith({ name: 'Spaced', icon: DEFAULT_DESIGN_ICON })
+  })
+
+  it('prefills name and icon in edit mode', () => {
+    const { onSubmit } = renderModal({
+      initial: { name: 'Existing', icon: 'server' },
+      title: 'Edit Canvas',
+      submitLabel: 'Save',
+    })
+    expect(screen.getByLabelText('Name')).toHaveValue('Existing')
+    // The server icon button is pre-selected.
+    expect(screen.getByRole('button', { name: 'Server' })).toHaveAttribute('aria-pressed', 'true')
+    fireEvent.click(screen.getByRole('button', { name: 'Save' }))
+    expect(onSubmit).toHaveBeenCalledWith({ name: 'Existing', icon: 'server' })
+  })
+
+  it('submits on Enter from the name field', () => {
+    const { onSubmit } = renderModal()
+    const input = screen.getByLabelText('Name')
+    fireEvent.change(input, { target: { value: 'Quick' } })
+    fireEvent.keyDown(input, { key: 'Enter' })
+    expect(onSubmit).toHaveBeenCalledWith({ name: 'Quick', icon: DEFAULT_DESIGN_ICON })
+  })
+
+  it('calls onClose from Cancel', () => {
+    const { onClose, onSubmit } = renderModal()
+    fireEvent.click(screen.getByRole('button', { name: 'Cancel' }))
+    expect(onClose).toHaveBeenCalled()
+    expect(onSubmit).not.toHaveBeenCalled()
+  })
+})