dnd5e: Spellbook tab revisions for dnd5e 4.0 - more formal class filter, separate statistics cards for multiclassing, spell slot summary

[kgar]

Spell Atk and DC are now represented individually for each spell class via actor.classes[].spellCasting

• The stock spellcasting fields in system.attributes represent the primary spellcasting class, else generic calculations
• Actors with classes: use class calculations
• Actors without classes: use generic calculations
• Primary Spellcasting Ability: use toggle like the default sheets.

MVP:
Ensure that whichever class is chosen in the class filter, the spell Atk and DC reflect this change.

Ideal:
Set up a subtab or class selector that is native and not hidden behind a setting to allow filtering the spellbook.
Migrate the Atk, DC, and Prepared Value/Max to a spellcasting card, similar to / same as the default character sheet.
Give NPCs the same treatment.
The spell Atk should be rollable, as it always has been, but consider what UI makes the most sense to provide an accessible cue that the Atk is rollable.
Stretch: show a consolidated representation of spell slots, potentially with the Epic Boon Roman Numeral setup from the default sheets, and similar to the style of Baldur's Gate 3. The goal is to give a quick look at how many spell slots the caster class has total, without having to scroll, own spells of the appropriate level, etc.