Module inspector 

Widget inspector panel — uses the system TreeView for tree display.

Layout (Y-up, panel fills its full bounds):

┌─────────────────────┐ ← top (HEADER_H)   header (painted monolithically)
├─────────────────────┤
│   TreeView          │ ← tree area (TreeView painted here)
├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┤ ← draggable h-split
│   Properties        │ ← props area (painted monolithically)
└─────────────────────┘ ← bottom (y=0)

Structs

InspectorPanel

InspectorSavedState

Serializable inspector UI state — apply at startup, snapshot at shutdown.