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 <noreply@anthropic.com>

src/scene/model/hatch_patterns.rs

@@ -0,0 +1,88 @@
+// OpenCADStudio hatch pattern catalog — built from `assets/patterns/OpenCADStudio.pat`.
+//
+// Each `PatternEntry` wraps a parsed PAT pattern with:
+//   - `gpu`       — `HatchPattern::Pattern(families)` for the shader
+//   - `pat_lines` — exact PAT line definitions used for DXF export
+
+use std::sync::OnceLock;
+
+use crate::patterns::PatLineDef;
+use crate::scene::model::hatch_model::{HatchPattern, PatFamily};
+use acadrust::entities::{HatchPattern as DxfPattern, HatchPatternLine};
+use acadrust::types::Vector2;
+
+// ── Public types ──────────────────────────────────────────────────────────
+
+pub struct PatternEntry {
+    pub name: String,
+    pub description: String,
+    /// GPU-ready pattern for the shader.
+    pub gpu: HatchPattern,
+    /// Exact PAT line families (used for DXF export).
+    pub pat_lines: Vec<PatLineDef>,
+}
+
+// ── Catalog ───────────────────────────────────────────────────────────────
+
+static CATALOG: OnceLock<Vec<PatternEntry>> = OnceLock::new();
+
+pub fn catalog() -> &'static [PatternEntry] {
+    CATALOG.get_or_init(build_catalog)
+}
+
+pub fn find(name: &str) -> Option<&'static PatternEntry> {
+    catalog().iter().find(|e| e.name.eq_ignore_ascii_case(name))
+}
+
+pub fn names() -> Vec<String> {
+    catalog().iter().map(|e| e.name.clone()).collect()
+}
+
+// ── DXF export ────────────────────────────────────────────────────────────
+
+pub fn build_dxf_pattern(entry: &PatternEntry) -> DxfPattern {
+    let mut pat = DxfPattern::new(&entry.name);
+    pat.description = entry.description.clone();
+    for ln in &entry.pat_lines {
+        let angle_rad = (ln.angle_deg as f64).to_radians();
+        pat.lines.push(HatchPatternLine {
+            angle: angle_rad,
+            base_point: Vector2::new(ln.x0 as f64, ln.y0 as f64),
+            offset: Vector2::new(ln.dx as f64, ln.dy as f64),
+            dash_lengths: ln.dashes.iter().map(|&d| d as f64).collect(),
+        });
+    }
+    pat
+}
+
+// ── Builder ───────────────────────────────────────────────────────────────
+
+fn build_catalog() -> Vec<PatternEntry> {
+    let mut entries = vec![PatternEntry {
+        name: "SOLID".into(),
+        description: "Solid fill".into(),
+        gpu: HatchPattern::Solid,
+        pat_lines: vec![],
+    }];
+
+    for def in crate::patterns::catalog() {
+        entries.push(PatternEntry {
+            name: def.name.clone(),
+            description: def.description.clone(),
+            gpu: HatchPattern::Pattern(def.lines.iter().map(pat_line_to_family).collect()),
+            pat_lines: def.lines.clone(),
+        });
+    }
+    entries
+}
+
+fn pat_line_to_family(ln: &PatLineDef) -> PatFamily {
+    PatFamily {
+        angle_deg: ln.angle_deg,
+        x0: ln.x0,
+        y0: ln.y0,
+        dx: ln.dx,
+        dy: ln.dy,
+        dashes: ln.dashes.clone(),
+    }
+}