Add Comic Book Builder preview mode and shareable HTML export

[Copilot]

The Comic Book Builder could generate panels and export raw project JSON, but it did not provide a read-through preview of the comic or a simple artifact for sharing completed work. This change adds an in-app preview flow and a standalone HTML export/share path.

• Preview-first reading flow

  • Adds a dedicated Preview tab to review the comic page-by-page before export.
  • Renders generated panel art with dialogue overlays in reading order.
  • Surfaces incomplete panels with placeholders so unfinished pages are still inspectable.

• Shareable comic output

  • Adds standalone HTML preview export for a portable, human-readable comic artifact.
  • Adds native share support where available, with HTML download fallback when platform sharing is unavailable.
  • Keeps existing JSON export for source/project interchange.

• Export generation

  • Introduces a focused HTML document builder for comic projects.
  • Escapes user-authored content before embedding it into exported markup.

• UI updates

  • Extends Comic Book Builder navigation and export actions to include preview and sharing paths.
  • Adds preview-specific layout/styling for pages, panels, placeholders, and dialogue summaries.

const file = new File([buildComicHtmlDocument(project)], `${slug}-comic-preview.html`, {
  type: "text/html",
});

await navigator.share({
  title: `${project.title} comic preview`,
  text: `Sharing ${project.title} as a standalone comic preview.`,
  files: [file],
});

[Copilot]

Pull request overview

Adds an in-app “Preview” reading flow for Comic Book Builder projects and introduces a shareable standalone HTML export path (alongside existing JSON export), enabling page-by-page review and easy sharing of completed comics.

Changes:

• Added buildComicHtmlDocument() HTML document generator with user-content escaping and panel/dialogue rendering.
• Introduced a new Preview tab UI (ComicPreview) to review pages/panels (including placeholders for unfinished panels).
• Expanded export UI to support JSON export, HTML export, and native share (with download fallback), plus new preview/export styling.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/features/comic-builder/export-html.ts	New standalone HTML builder for comic previews, including escaping and styling.
src/features/comic-builder/export-html.test.ts	Vitest coverage for HTML generation and escaping behavior.
src/features/comic-builder/components/ComicPreview.tsx	New Preview tab component to render pages/panels and dialogue overlays in-app.
src/features/comic-builder/ComicBuilderStudio.tsx	Adds Preview tab, HTML export + share actions, and refactors download logic.
src/features/comic-builder/comic-builder.css	Adds preview/export layout styles for the new UI sections.

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