refactor(scene): group modules into role-based subfolders

Move the 30 flat modules under src/scene/ into six folders by role:
convert (entity→geometry), text (fonts/shaping), model (render models),
pick (hit-test/selection/grips/xclip), view (camera/transform/render),
cache (block + property caches). pipeline/ is unchanged.

Full path migration — all `scene::X` references become
`scene::<group>::X`, no compatibility re-exports. render.rs items that
were `pub(super)` (parent was scene) become `pub(in crate::scene)` to
keep their original scene-wide visibility.

No behavior change; build and tests are green.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/scene/cache/mod.rs

@@ -0,0 +1,2 @@
+pub mod block_cache;
+pub mod properties;

src/scene/cache/properties.rs

@@ -0,0 +1,69 @@
+use acadrust::{EntityType, Handle};
+
+use crate::scene::model::object::{PropSection, PropValue, Property};
+
+pub fn general_section(entity: &EntityType) -> PropSection {
+    let common = entity.common();
+    let linetype_display = if common.linetype.is_empty() {
+        "ByLayer".to_string()
+    } else {
+        common.linetype.clone()
+    };
+    let transp_pct = (common.transparency.alpha() as f64 / 255.0 * 100.0).round() as u32;
+
+    PropSection {
+        title: "General".into(),
+        props: vec![
+            Property {
+                label: "Layer".into(),
+                field: "layer",
+                value: PropValue::LayerChoice(common.layer.clone()),
+            },
+            Property {
+                label: "Color".into(),
+                field: "color",
+                value: PropValue::ColorChoice(common.color),
+            },
+            Property {
+                label: "Linetype".into(),
+                field: "linetype",
+                value: PropValue::LinetypeChoice(linetype_display),
+            },
+            Property {
+                label: "LT Scale".into(),
+                field: "linetype_scale",
+                value: PropValue::EditText(format!("{:.4}", common.linetype_scale)),
+            },
+            Property {
+                label: "Lineweight".into(),
+                field: "lineweight",
+                value: PropValue::LwChoice(common.line_weight),
+            },
+            Property {
+                label: "Transparency".into(),
+                field: "transparency",
+                value: PropValue::EditText(format!("{transp_pct}")),
+            },
+            Property {
+                label: "Invisible".into(),
+                field: "invisible",
+                value: PropValue::BoolToggle {
+                    field: "invisible",
+                    value: common.invisible,
+                },
+            },
+        ],
+    }
+}
+
+pub fn fallback_properties(_handle: Handle, entity: &EntityType) -> PropSection {
+    PropSection {
+        title: "Geometry".into(),
+        props: vec![Property {
+            label: "Type".into(),
+            field: "type",
+            value: PropValue::ReadOnly(crate::entities::names::ui_name(entity).into()),
+        }],
+    }
+}
+