Shaders: Slice C — GUI thumbnails + stylized tunables

[fernandotonon]

Part of #743 (Epic: Shaders). Depends on Slice B.

Goal

Surface the stylized presets and their key tunables in the Inspector. The thumbnail grid auto-lists new names; this slice adds the knobs stylized looks need.

Work

• qml/PropertiesPanel.qml Material Presets section (~4200–4237): generate sphere-preview thumbnails for the new presets the same way existing presets do.
• Add a small "Stylized" subsection (or extend the preset section) that exposes the high-value params when a stylized preset is active: toon band count, outline width + color, rim color + power, matcap texture picker.
• Bind through new MaterialPresetLibrary Q_INVOKABLE setters, or reuse MaterialEditorQML pass props where they map cleanly (e.g. cull / polygon mode for outline).

Acceptance

• New presets show thumbnails in the grid.
• Selecting a stylized preset reveals its relevant tunables; editing a tunable updates the viewport live.
• Tunables are no-ops / hidden for non-stylized presets.