ModularShoot

Added

• Install API supports a preferred plugin category: installPlugin gained an optional preferred-type parameter (e.g. a plugin panel dragging a plugin onto a category area). A matching hint installs directly into that category; a miss falls back to the original auto-selection. Existing callers are unaffected.
• Effective-slot query facade: new getEffectiveSlots API returns each category's effective capacity (including installed plugins' adds_slots), so UIs can render install areas without re-implementing the aggregation.