Add offsetFirstPage preference for fixed-layout EPUBs

[mickael-menu]

Summary

• Adds offsetFirstPage preference to control whether the first page of a fixed-layout EPUB is displayed alone (centered) or alongside the second page when spreads are enabled.
  • When true, first page displays alone; when false, pairs with second page; when nil, uses publication metadata
• Significant refactoring of the EPUBSpread models.

Changelog

Added

Navigator

• Added offsetFirstPage preference for fixed-layout EPUBs to control whether the first page is displayed alone or alongside the second page when spreads are enabled.

[Copilot]

Pull request overview

This PR adds a new offsetFirstPage preference for fixed-layout EPUBs that controls whether the first page is displayed alone (centered) or alongside the second page when spreads are enabled. The implementation includes a significant refactoring of the EPUBSpread models from a struct-based design to a protocol-based enum design with distinct single and double spread types.

Changes:

• Added offsetFirstPage preference (nullable Bool) for EPUB fixed-layout and PDF navigators
• Refactored EPUBSpread from a struct to an enum with EPUBSingleSpread and EPUBDoubleSpread types implementing a common EPUBSpreadProtocol
• Updated UI to support nullable boolean preference picker with "Auto", "Yes", and "No" options

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Sources/Navigator/EPUB/EPUBSpread.swift	Major refactoring to protocol-based enum design; added offsetFirstPage parameter to spread creation logic
Sources/Navigator/EPUB/Preferences/EPUBPreferences.swift	Added offsetFirstPage: Bool? property to preferences model
Sources/Navigator/EPUB/Preferences/EPUBPreferencesEditor.swift	Added preference editor for offsetFirstPage with appropriate effectiveness conditions
Sources/Navigator/EPUB/Preferences/EPUBSettings.swift	Added offsetFirstPage: Bool? to settings and initialization
Sources/Navigator/EPUB/EPUBSpreadView.swift	Updated to use refactored spread model with spread.first.link
Sources/Navigator/EPUB/EPUBReflowableSpreadView.swift	Updated to use spread.first.link instead of direct reading order access
Sources/Navigator/EPUB/EPUBFixedSpreadView.swift	Updated to pass readingProgression to JSON generation
Sources/Navigator/EPUB/EPUBNavigatorViewModel.swift	Added offsetFirstPage property accessor
Sources/Navigator/EPUB/EPUBNavigatorViewController.swift	Removed force parameter from reload logic; passes offsetFirstPage to spread creation
Sources/Navigator/PDF/Preferences/PDFPreferences.swift	Updated documentation for offsetFirstPage
Sources/Navigator/PDF/Preferences/PDFPreferencesEditor.swift	Updated documentation for offsetFirstPage
TestApp/Sources/Reader/Common/Preferences/UserPreferences.swift	Added nullableOffsetFirstPage parameter and nullableBoolPickerRow UI component
CHANGELOG.md	Documented the new feature

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