Introduce bookmark Categories as a second organisational dimension with automatic Color and Icon assignment

[vitekslv]

Currently, bookmarks are organised into folders, which works well for grouping by trip, location, or project. Individual bookmarks can already have a custom color, but assigning them manually one by one offers no systematic visual consistency by bookmark type — there is no way to say "all restaurants should be red" and have that applied automatically across folders.

I'd like to propose a category system that works orthogonally to folders:

• Folders answer where/when — "Trip to Fuerteventura", "Riga everyday", "Hikes 2025"
• Categories answer what — "Beach", "Restaurant", "Viewpoint", "Accommodation"

Each bookmark belongs to one folder (as today) and optionally to one category. The category defines the marker color and icon shown on the map. This way, across any folder, all restaurants appear red, all beaches blue, all viewpoints green — without changing how folders work at all.

Why not just use separate folders per type?
That forces a choice: organise by trip or by type — you can't have both. With categories, you get both dimensions simultaneously. A bookmark in "Trip to Fuerteventura" can be visually identified as a "Restaurant" on the map without leaving that folder.

KML/GPX implementation — fully backward compatible
The category metadata can be stored using a custom XML namespace in existing KML/GPX files, following the same pattern Organic Maps already uses with the mwm: namespace.

User-facing behaviour

• A new Categories screen (similar to the existing color/icon picker) where users can create and manage categories, each with a name, color, and default icon.
• When adding or editing a bookmark, an optional Category picker appears alongside the existing folder selector.
• Optionally: a filter in the bookmark list and/or map view to show/hide bookmarks by category.

This would make the bookmark system genuinely two-dimensional without breaking any existing workflow or file format compatibility.

[biodranik]

Related: #4766

The main challenge is making it easy-to-use for everyone.

[vitekslv]

I completely understand that maintaining a simple, clutter-free experience is a major challenge, and I wouldn't want to compromise what makes the app so great.

As a middle-ground that might be easier to implement, would you consider allowing users to simply rename the bookmark color labels? Instead of the fixed names like 'Red' or 'Blue,' a user could rename 'Red' to 'Restaurants' and 'Blue' to 'Beaches.' This would essentially allow the existing color system to act as a categorization layer without adding any new screens or complex database structures.

Organic Maps is one of the few navigation apps left with a truly excellent minimal design. Because the interface is so clean, I believe it has the 'visual room' to support more than one dimension of organization. Adding this second layer (What/Category) alongside the first (Where/Folder) would provide the depth that power users need while keeping the UI intuitive for everyone else.