feat: calculator widget v61 + OS widget

[ovitrif]

Description

This PR:

1. Refreshes the in-app Calculator widget with the v6.1 row/card treatment and Bitkit number pad flow.
2. Adds a native iOS Home Screen Calculator widget for small and medium families, backed by App Group mirrored calculator values and currency settings.
3. Adds the Calculator v61 preview carousel, focused formatter/input coverage, and the user-facing changelog fragment.

Mirrors the v61 calculator app and OS widget work from bitkit-android#942.

Linked Issues/Tasks

N/A

Screenshot / Video

VIDEO_1

QA Notes

Manual Tests

• 1. Widgets → Bitcoin Calculator: small and wide previews render the v6.1 two-row calculator card.
• 2. Home → Calculator widget → tap Bitcoin row: Bitkit number pad opens, modern Bitcoin uses space grouping, invalid input flashes the pressed key red, and fiat conversion updates.
• 3. Home → Calculator widget → tap fiat row: Bitkit number pad opens, fiat grouping uses commas, one-decimal input shows the dimmed trailing zero placeholder, and Bitcoin conversion updates.
• 4. regression: Settings → General → Default Unit → switch Modern/Classic: Calculator preserves the Bitcoin amount while changing denomination formatting.
• 5. Home Screen → add Bitkit Calculator small widget: two read-only rows render without trailing labels.
• 6. Home Screen → add Bitkit Calculator medium widget: two read-only rows render with Bitcoin and fiat labels.
• 7. Home Screen → tap Calculator OS widget: Bitkit opens without auto-focusing calculator input.

Automated Checks

• Unit tests added: BitkitTests/CalculatorWidgetTests.swift covers calculator grouping, decimal placeholder behavior, number-pad delete/decimal caps, localized comma input normalization, symbol shortening, and classic BTC-to-sats conversion.
• Local: swiftformat Bitkit/Models/CalculatorWidgetData.swift Bitkit/Services/Widgets/CalculatorHomeScreenWidgetOptionsStore.swift Bitkit/Components/Widgets/CalculatorWidget.swift Bitkit/Components/NumberPad.swift Bitkit/Views/Widgets/CalculatorWidgetPreviewView.swift BitkitWidget/CalculatorHomeScreenWidget.swift BitkitTests/CalculatorWidgetTests.swift Bitkit/Models/Currency.swift Bitkit/MainNavView.swift BitkitWidget/BitkitWidget.swift
• Local: node scripts/validate-translations.js
• Local: xcodebuild -workspace Bitkit.xcodeproj/project.xcworkspace -scheme Bitkit -configuration Debug -destination 'platform=iOS Simulator,name=iPhone 16 Pro,OS=18.5' build
• Local: xcodebuild -workspace Bitkit.xcodeproj/project.xcworkspace -scheme Bitkit -configuration Debug -destination 'platform=iOS Simulator,id=8E6C558B-8483-4237-920D-C16B69D61B51,arch=arm64' -only-testing:BitkitTests/CalculatorWidgetTests build-for-testing
• Local simulator launch: installed the built app on iPhone 16 Pro iOS 18.5 after removing the known static LDKNodeFFI.framework build artifact stub from DerivedData, then launched to.bitkit successfully.
• Attempted: xcodebuild ... -only-testing:BitkitTests/CalculatorWidgetTests test compiled but could not execute because simulator app installation failed on the existing LDKNodeFFI.framework static-framework bundle stub.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use a static calculator widget description

The home-screen widget gallery cannot perform the app's t(..., variables:) substitution here, but widgets__calculator__description is the in-app string that contains {fiatSymbol}. As a result, when users add the new Calculator OS widget from the iOS widget gallery, the description is shown with the literal {fiatSymbol} placeholder instead of a real currency symbol or generic text.

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