chore(test): add tab-item-icon appearance scenario for iOS

[LKuchno]

Description

Adds a new manual test scenario (test-tabs-item-icon-ios) that exercises the iOS tab bar item icon color props exposed on TabsScreen. The scenario covers four distinct icon configuration cases: templateSource (tintable, check with host tint), sfSymbol with tabBarItemIconColor override, xcasset (tintable, check with host tint), and imageSource (non-tintable). It verifies that standardAppearance.stacked.selected.tabBarItemIconColor correctly overrides the host-level tabBarTintColor for the selected icon color, and that imageSource icons are non-tintable and unaffected by either prop.

This is iOS-only. Automated Detox assertions are not feasible because Detox does not expose tint color or rendered image attributes of native tab bar items. Known behavioral differences between iOS 18 and iOS 26 are documented in the scenario notes.

Closes: https://github.com/software-mansion/react-native-screens-labs/issues/1399

Changes

• Tests/Tabs: Added test-tabs-item-icon-ios/index.tsx - new test screen with four tab routes exercising templateSource host-tint, sfSymbol with tabBarItemIconColor override, xcasset host-tint, and non-tintable imageSource icon
• Tests/Tabs: Added scenario-description.ts registering the scenario as iOS-only, e2eCoverage: 'incomplete', smokeTest: false
• Tests/Tabs: Added scenario.md with full manual test steps, iOS 18 vs iOS 26 known-issue callouts, and per-step verification checklists
• Tests/Tabs: Registered TestTabsItemIcon in apps/src/tests/single-feature-tests/tabs/index.ts

[Copilot]

Pull request overview

Adds an iOS-only manual test scenario for validating tab bar item icon appearance behavior across different TabsScreen icon sources and tint/override configurations.

Changes:

• Adds a new test-tabs-item-icon-ios scenario implementation and metadata.
• Documents manual verification steps for tintable and non-tintable icon cases.
• Registers the scenario in the Tabs single-feature test group.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
apps/src/tests/single-feature-tests/tabs/test-tabs-item-icon-ios/index.tsx	Implements the four-tab manual scenario and icon configurations.
apps/src/tests/single-feature-tests/tabs/test-tabs-item-icon-ios/scenario-description.ts	Defines scenario metadata and iOS-only coverage status.
apps/src/tests/single-feature-tests/tabs/test-tabs-item-icon-ios/scenario.md	Adds manual test instructions and expected results.
apps/src/tests/single-feature-tests/tabs/index.ts	Registers the new scenario in the Tabs group.

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[LKuchno]

PR closed as new screen for both platforms were implemented and introduced in #4108