revert: drop zigbee LQI edge coloring and path highlighting

Split out of this PR — will land separately with reworked zigbee edge
capture/storage. Keeps only the floor plan + generic media upload work.

- Remove getLqiColor + LQI-derived iot edge stroke (edges/index.tsx)
- Remove zigbee path highlight effect (DetailPanel.tsx)
- Remove highlightedPath/setHighlightedPath store state (canvasStore.ts)
- Delete utils/zigbeePathfinding.ts
- Revert associated test scaffolding and package-lock churn

frontend/src/stores/canvasStore.ts

@@ -38,8 +38,6 @@ interface CanvasState {
   floorMap: FloorMapConfig | null
   setFloorMap: (config: FloorMapConfig | null) => void
   updateFloorMap: (patch: Partial<FloorMapConfig>) => void
-  highlightedPath: string[]
-  setHighlightedPath: (edgeIds: string[]) => void
 
   // History
   past: HistoryEntry[]
@@ -105,7 +103,6 @@ export const useCanvasStore = create<CanvasState>((set) => ({
   scanEventTs: 0,
   serviceStatuses: {},
   floorMap: null,
-  highlightedPath: [],
   fitViewPending: false,
 
   past: [],
@@ -763,8 +760,6 @@ export const useCanvasStore = create<CanvasState>((set) => ({
       hasUnsavedChanges: true,
     })),
 
-  setHighlightedPath: (edgeIds) => set({ highlightedPath: edgeIds }),
-
   loadCanvas: (nodes, edges) => {
     // React Flow requires parents before children in the array
     const parents = nodes.filter((n) => !n.parentId)