Remove vestigial code from NFC/Scan removal

[dadachi]

Mirror of upstream nativeapptemplate/NativeAppTemplate-iOS#67, adapted to this fork.

Summary

Cleanup of dead code left behind after the NFC/QR/Scan feature was removed:

• Delete CustomerScannedTag view — zero call sites, only referenced itself. Drop the corresponding customerScannedTag{Background,Border,Foreground} colors from Color+Extensions.swift and the file refs from project.pbxproj.
• Drop preparingTag{Background,Border,Foreground} colors — no view ever referenced them; vestigial from an older item-state hierarchy.
• MainButtonView.swift: remove a 3-line dead comment about a Scan-tab accessibility workaround that no longer applies.
• CodedError.swift: remove the NFC mention from the error-code range comment; no error type uses that range anymore.

Net diff: 5 files, −78 / +1. No behavior change, no public API touched, no tests modified.

Test plan

• make lint passes
• xcodebuild ... build-for-testing succeeds (iPhone 17, iOS 26.4.1)
• Run tests in Xcode (Cmd+U)
• Smoke-check Shop Detail / ItemTag list views still render the IdlingTag / CompletedTag correctly

Notes

• IdlingTag was almost deleted because the file is named IdlingTagView.swift while the struct is named IdlingTag — the initial grep missed callers. Verified IdlingTag() is referenced from ShopDetailCardView, ItemTagListCardView, and ItemTagDetailView and kept intact.

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