feat: add logo, favicon, and theme system

- Add custom SVG favicon and Logo component (house + network nodes motif)
- Update page title to Homelable with meta description
- Show Logo in sidebar header and toolbar
- Add theme store and ThemeModal for canvas style switching
- Refactor node colors and edge styles for theme support

frontend/src/stores/__tests__/themeStore.test.ts

@@ -0,0 +1,31 @@
+import { describe, it, expect, beforeEach } from 'vitest'
+import { useThemeStore } from '@/stores/themeStore'
+
+describe('themeStore', () => {
+  beforeEach(() => {
+    useThemeStore.setState({ activeTheme: 'default' })
+  })
+
+  it('starts with default theme', () => {
+    expect(useThemeStore.getState().activeTheme).toBe('default')
+  })
+
+  it('setTheme updates activeTheme', () => {
+    useThemeStore.getState().setTheme('matrix')
+    expect(useThemeStore.getState().activeTheme).toBe('matrix')
+  })
+
+  it('setTheme can switch between all presets', () => {
+    const themes = ['default', 'dark', 'light', 'neon', 'matrix'] as const
+    for (const id of themes) {
+      useThemeStore.getState().setTheme(id)
+      expect(useThemeStore.getState().activeTheme).toBe(id)
+    }
+  })
+
+  it('setTheme back to default after neon', () => {
+    useThemeStore.getState().setTheme('neon')
+    useThemeStore.getState().setTheme('default')
+    expect(useThemeStore.getState().activeTheme).toBe('default')
+  })
+})

frontend/src/stores/canvasStore.ts

@@ -32,6 +32,7 @@ interface CanvasState {
   editingGroupRectId: string | null
   setEditingGroupRectId: (id: string | null) => void
   markSaved: () => void
+  markUnsaved: () => void
   loadCanvas: (nodes: Node<NodeData>[], edges: Edge<EdgeData>[]) => void
   notifyScanDeviceFound: () => void
 }
@@ -155,6 +156,8 @@ export const useCanvasStore = create<CanvasState>((set) => ({
 
   markSaved: () => set({ hasUnsavedChanges: false }),
 
+  markUnsaved: () => set({ hasUnsavedChanges: true }),
+
   notifyScanDeviceFound: () => set({ scanEventTs: Date.now() }),
 
   loadCanvas: (nodes, edges) => {

frontend/src/stores/themeStore.ts

@@ -0,0 +1,12 @@
+import { create } from 'zustand'
+import type { ThemeId } from '@/utils/themes'
+
+interface ThemeState {
+  activeTheme: ThemeId
+  setTheme: (id: ThemeId) => void
+}
+
+export const useThemeStore = create<ThemeState>((set) => ({
+  activeTheme: 'default',
+  setTheme: (id) => set({ activeTheme: id }),
+}))