Campaign-level toggle (CharacterManager, live flip). When ON, ending an
encounter writes each character participant's current HP, Max HP, and AC back
to the campaign roster so they carry into the next encounter.
- shared: buildCharacterParticipant uses defaultCurrentHp (fallback maxHp)
- endEncounter: syncs maxHp/ac/currentHp to campaign players if syncCharacters,
snapshots old values into undo payload for restore. Works retroactive
(ctx.campaignId fallback for encounters lacking campaignId field).
- New encounters store campaignId field.
- Undo end-encounter restores character values client-side.
- CharacterManager: styled sync toggle (checkbox badge), stat badges in list
(HP/Current HP/AC/Init), edit box supports Current HP field.
Tests: 5 writeback cases (off/on/skip monsters/undo snapshot/missing char).
