BL-15958 Rename ebook theme to edge-to-edge, expand to all page sizes

[hatton]

[Claude Opus 5.5 from Hatton's machine during preflight]

Part 1 of 3 of the BL-15958 work. The other two are the full-bleed page sizes (#8263) and the edit-mode crop marks (#8264).

Problem

The "Zero Margin Ebook" page theme takes pictures to the page edge, but only on ebook and device page sizes. Full-bleed print books need the same at any paper size, and once the theme is used for print its name no longer describes it.

What the PR does

• Renames the theme to Edge to Edge. A book that stores the old name zero-margin-ebook is read and saved as edge-to-edge (AppearanceSettings.NormalizeThemeName). The eBook and Playground templates and the EFL ebook migration use the new name.
• Applies the theme to every page size. Numbered content pages have no margin; front and back matter keep 3mm.
• With full bleed on, text boxes stay 3mm inside the trimmed edge. Page numbers placed left or right line up with the text and shift with the trim offset (new --pageNumber-side-left-inset / --pageNumber-side-right-inset).
• Keeps master's format-button placement on the theme's ebook pages (BL-14901): the button moves clear of a bottom-left page number on landscape pages and stays put on portrait pages, where the number is centered.
• The full-bleed help text in Book Settings now names the theme. The theme label and that help text get new translatable string ids (AppearanceTheme.edge-to-edge, BookSettings.FullBleed.Description.EdgeToEdge). The old entries are kept and marked obsolete as of 6.6.

Screenshots

None captured yet. The theme has not been looked at in a running Bloom since master was merged in; the checks are in the test-ideas comment on BL-15958.

Risk Evaluation

• appearance-theme-edge-to-edge.css now matches every numbered page instead of the four Ebook/Device sizes, so any book using the theme at a paper size changes layout. This includes existing books, which lose their content-page margins without the user doing anything. That is deliberate.
• The page-number override formula in AppearanceSettings.SetPageNumberProperties runs for every book whose user forces page numbers left or right. It now reads --pageNumber-side-left-inset / --pageNumber-side-right-inset, which fall back to the page margin, so other themes are unchanged.
• pageNumbers.less and pageBoxesSizing.less: the full-bleed bottom offset moves into its own variable, --pageNumber-full-bleed-bottom-adjustment. That affects page-number placement in every full-bleed book.
• basePage.less adds text-box insets that are 0mm unless the theme sets them.

Ecosystem Impact

• Published output and Bloom Player: the theme stylesheet travels with the book, so BloomPUB, ePUB and PDF get the new layout. Not checked by hand.
• Older Bloom versions: a book saved by this build stores edge-to-edge, a theme name an older Bloom does not have. What an older Bloom then shows was not checked.
• Localization: two new translatable strings reach Crowdin. The old ones stay, marked obsolete. Until translators catch up, the theme label and the full-bleed help show in English. Non-English XLF files are untouched.
• Docs: the docs site's Page Themes Catalog and Bloom's Built-in Book Templates pages still say "Zero Margin Ebook".

E2E Coverage

No end-to-end test covers this theme. The visual-regression theme list (src/BloomVisualRegressionTests/index.spec.ts) now names edge-to-edge. That suite was not run for this PR.

Notion Test Suite

This PR added or changed no cards. The existing "Zero Margin Device Theme" cards in Test Case Runs describe the old name and say the theme only applies to Ebook/Device layouts.

Ref: BL-15958

🤖 Generated with Claude Code

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Devin review

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This change is 

[greptile-apps]

Greptile Summary

This PR renames the zero-margin ebook appearance theme to Edge to Edge, normalizes the legacy theme ID, and extends its margin and page-number behavior to all page sizes.

• Adds legacy-to-canonical theme-name normalization in AppearanceSettings.
• Renames and broadens the appearance-theme CSS, including full-bleed text and page-number insets.
• Updates templates, migration data, tests, and localization catalogs for the new theme name.

Important Files Changed

Filename	Overview
src/BloomExe/Book/AppearanceSettings.cs	Normalizes the legacy theme alias on loading, assignment, and CSS generation, and updates explicit side-page-number formulas.
src/content/appearanceThemes/appearance-theme-edge-to-edge.css	Renames the theme, applies zero margins across page sizes, and introduces full-bleed text and page-number inset rules.
src/content/bookLayout/basePage.less	Adds an inset frame for top-level translation groups so full-bleed text can remain within the safe area.
src/content/bookLayout/pageNumbers.less	Refactors the full-bleed bottom offset into a separately composed CSS variable.
DistFiles/localization/en/BloomMediumPriority.xlf	Renames an established trans-unit ID, which breaks the repository’s localization identity and retirement workflow.
DistFiles/localization/es/BloomMediumPriority.xlf	Directly rewrites a Crowdin-owned locale while retaining an approved translation for the old theme meaning under the new key.
src/BloomTests/Book/AppearanceSettingsTests.cs	Updates expectations for canonical theme naming and the new page-number inset formulas.
src/BloomVisualRegressionTests/index.spec.ts	Replaces the old theme ID with the canonical ID in the visual-regression theme matrix.

_{Reviews (1): Last reviewed commit: "BL-15958 Rename ebook theme to edge-to-e..." | Re-trigger Greptile}

[hatton]

[Claude Opus 5.5 from Hatton's machine during preflight] @greptile-apps review

[greptile-apps]

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[hatton]

Decided: leave as is. The three BL-15958 PRs (#8262, #8263, #8264) target master deliberately. The card has no [6.5] prefix, so it names no release branch.

[Devin] Investigate: Wrong release branch target (AGENTS.md, outside the diff, so not resolvable as a thread)

This PR targets master despite the temporary Version6.5 mandate in AGENTS.md. Retarget it or document an explicit exception before merging.

[hatton]

[Claude Opus 5.5 from Hatton's machine during preflight] Consulted Devin on 2026-10-06 up to commit 3da2bb4. It raised one bug and two investigate flags that apply to the current code: two are answered and resolved on their threads, and the release-branch question is open for the developer. Four more findings described the earlier commit 66fb4d1 (edited non-English XLF files, the damaged Portuguese file, the renamed theme id) and are fixed in 3da2bb4. Two informational notes, not posted.

[hatton]

[Claude Opus 5.5 from Hatton's machine during preflight] On Devin's release-branch flag (#8262 (comment)): the developer decided to keep master as the base. The three BL-15958 PRs (#8262, #8263, #8264) are one chain built on master, and the card has no [6.5] prefix, so it names no release branch.

[StephenMcConnel]

@StephenMcConnel reviewed 56 files and all commit messages, and resolved 2 discussions.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on hatton).