Add camera switch button to barcode scanner

[gamerg21]

Motivation

• Provide users with an explicit way to choose between multiple cameras (front/rear) when the device exposes more than one video input.
• Improve reliability when the browser randomly chooses a camera by allowing an immediate manual switch.

Description

• Track available cameras with videoDevices and store the active camera in selectedDeviceId in BarcodeScanner.tsx.
• Add a Switch camera button (with RefreshCcw icon) that cycles the selected device via handleSwitchCamera when more than one camera is present.
• Restart the decoder when the selected camera changes by adding selectedDeviceId to the scanner useEffect dependencies and resetting the reader before reinitializing.
• Preserve the existing fallback behavior for environments that don't support device enumeration (e.g., iOS Safari) by falling back to the browser default camera.

Testing

• Ran type checking with npm run type-check which executed tsc --noEmit and passed.
• No other automated tests were added or run for this change.

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Fall back when selected camera is no longer available

The scanner now always prefers selectedDeviceId, but that value is persisted across openings and not checked against the freshly enumerated availableDevices. If the previously chosen camera was unplugged or permissions changed, decodeFromVideoDevice will be called with a stale device id and won’t fall back to the default camera, leaving the scanner stuck. Consider validating that selectedDeviceId still exists in availableDevices (or resetting it) before choosing activeDeviceId.

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