Fix camera setup review follow-ups

[berginj]

What changed

• points the documentation index to the current v2 FAQ
• replaces obsolete rolling-shutter webcam purchasing guidance with an evidence-first global-shutter qualification profile
• makes legacy pipeline camera defaults backend-aware: OpenCV uses indexes 0/1, while UVC and simulator backends retain logical IDs left/right
• adds regression tests for backend defaults and explicit overrides

Why

These changes address the still-valid review findings on PR #8 and PR #6. The old hardware guide could direct field testers toward unsuitable rolling-shutter cameras, and the OpenCV CLI failed at startup when its backend was selected without explicit camera indexes.

Validation

• 40 focused camera and CLI tests passed
• Flake8 passed repository-wide with zero findings
• file-length gate passed
• schema mirror check passed
• changed-document local links resolve
• git diff --check passed

Review references

• Align current documentation and recruit field testers #8 (comment)
• Align current documentation and recruit field testers #8 (comment)
• Add backend selection and camera ID options to pipeline CLI #6 (comment)

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Map legacy lane ROIs when defaulting OpenCV IDs

When --backend opencv is used without explicit IDs, these defaults change the runtime camera IDs to 0/1; if the operator still has a legacy configs/lane_roi.json keyed by left/right, load_lane_polygon() only checks the exact runtime IDs and silently falls back to the centered ROI. That makes the newly fixed default OpenCV path ignore saved lane calibration for those rigs, so either map the legacy left/right entries onto the numeric defaults or reuse the existing runtime ROI loader that has that fallback.

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