Allow toggling and reordering categories

[oczki]

• Add a new section under settings: Categories management.

Kategorie
[x] Miejsce         [v] [ ]
[x] Postać          [v] [^]
[ ] Cecha postaci   [v] [^]
[x] Emocja          [v] [^]
[ ] Relacja         [v] [^]
[ ] Czynność        [ ] [^]

Instead of buttons, this could be done based on dragging (with ⠿ icon as handler) and support touch events as well. Sounds like a fun challenge. (It isn't.)

• Allow reordering the items in this list.
• Propagate changes from this list into the real categories in <main> (reordering).
• Propagate changes from this list into the real categories in <main> (showing).
• Propagate changes from this list into the real categories in <main> (hiding).
• Animate the swap via some fancy CSS animations.
• To keep the gradient, colors will have to be assigned from top to bottom, not bound to specific categories.
• Handle a case where someone hides all categories. Maybe show a logo with direct link to category management and a separate link to revert to defaults.
• Check how it all works with a screen reader.
• Check how it all works in light and dark mode.
• Check how it all works with animations enabled and disabled.
• Add an indicator to the footer icon if any category is hidden. Use proper cutout around the dot.
• Add a counter to the panel's header. Kategorie (7/9)
• Prevent tabbing to hidden categories' buttons.
• Prevent tabbing to placeholder's two buttons if the placeholder is not shown.
• Resolve microcopy TODO (see comment below)

[oczki]

982c0f6 introduced a TODO to rewrite the microcopy of the 'restore all' button.

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Ideas

[ Przywróć domyślne kategorie ]
[ Pokaż listę kategorii ]

(that's a lot of repetition!)

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[ Pokaż listę kategorii ]
- albo -
[ Przywróć domyślne ]

(this looks better, but requires swapping the order of buttons)

[oczki]

The above was fixed by actually restoring every category to visible state. I believe this is a more sensible solution.