Offer more ready-made page backgrounds when creating a layout

[patriksimms]

Problem

As an organizer I only get two starting points when I create a page layout — a blank page and the geometric collage. Every other page has to be composed shape by shape, so most books end up either bare or reusing the same collage on every page.

Solution

Add two more ready-made backgrounds to the "Choose a background" dialog:

• Sunset arches — warm dusk band with overlapping arches on the right, leaving the left two thirds of the page free for text and photos.
• Postcard frame — a ruled postcard back with a divider, stamp block and address rules, for text-heavy pages.

Both are made from locked, axis-aligned rectangles and circles only, so they preview and print identically and can be unlocked and edited like the existing collage.

In-scope

• Two new background presets, selectable when creating a layout
• Picker layout adjusted so four options stay readable
• Analytics background_id stays in sync with the available presets

Out-of-scope

• Backgrounds with bound content, images or text elements
• Changing or restyling the existing blank and geometric collage presets
• Applying a background to an existing layout

Acceptance criteria

Initial state	Action	Result
Layouts tab open	Click "New layout"	Four backgrounds are offered: Blank, Geometric collage, Sunset arches, Postcard frame
Background dialog open	Click "Sunset arches"	A layout named "Sunset arches background" is created and selected, its decorative elements locked
Background dialog open	Click "Postcard frame"	A layout named "Postcard frame background" is created and selected, its decorative elements locked
New preset layout created	Open preflight / export	No bleed warnings: every preset element stays inside the media box