Parent: #1296
Depends on: #1299

Problem

The dashboard always displays real-time data for the first GPU only:

• DashboardItems.tsx matches GPU data to hardwareInfo.gpus?.[0]
• Doughnut charts and temperature display reflect only one GPU
• No way for users to switch between GPUs in the real-time view

Proposed Changes

1. Add GPU selector to dashboard GPU card

When hardwareInfo.gpus has more than one entry, display a selector (tabs or dropdown) in the GPU section header that writes to selectedGpuIdAtom.

For single-GPU systems, no selector is shown — behavior is identical to current.

2. Update real-time data binding

• Doughnut chart (GPU usage %) reads from the selected GPU's history via graphicUsageHistoryAtom (derived atom from [Frontend] Redesign atoms and event listener for multi-GPU #1299)
• Temperature display reads from gpuTempAtom filtered by selected GPU name
• Dedicated memory reads from gpuDedicatedMemoryKbMapAtom[selectedGpuId]
• Fan speed reads from gpuFanSpeedAtom filtered by selected GPU name

3. Update getTargetInfo helper

Currently returns hardwareInfo.gpus?.[0]. Should return the GPU matching selectedGpuIdAtom, falling back to gpus[0].

4. GPU info table

The info table already loops over hardwareInfo.gpus to display all GPUs — this stays the same.

Affected Files

• src/features/hardware/dashboard/components/DashboardItems.tsx
• Potentially src/features/hardware/usage/Usage.tsx (if GPU selector applies to usage page too)

UX Notes

• GPU selector should persist across page navigation (stored in selectedGpuIdAtom)
• Default selection: first GPU in the list
• Each GPU entry in the selector should show the GPU name (e.g., "AMD Radeon RX 7900 XTX", "AMD Radeon Graphics")