feat(viewer): stage thumbnail grid, per-model albedo, camera zoom fix

Route stage containers to stage_models (decode both single + stage paths, keep
whichever yields more geometry) — fixes stages showing the dummy-root "black
cube". Present a stage's sub-models as a thumbnail grid: each recentred and
uniformly scaled to a fixed cell so a 1-unit prop and a 3000-unit structure are
equally visible; skybox-plane / stray-anchor models (>20000u) are culled. Each
sub-model is textured by matching its name to the container's `_col` albedo.

Fix the orbit camera: zoom radius was hard-capped at 50u with fixed clip planes,
trapping the camera inside multi-thousand-unit stages. Zoom limits and near/far
planes now scale to the framed model.

Adds docs/HANDOFF-stage-mesh-2026-07-12.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/sylpheed-viewer/src/camera.rs

@@ -32,6 +32,10 @@ pub struct OrbitCamera {
     pub orbit_sensitivity: f32,
     pub zoom_sensitivity: f32,
     pub pan_sensitivity: f32,
+    /// Zoom limits — set when framing a model so large scenes can be pulled back
+    /// far enough (the old fixed 0.5..50 cap trapped the camera inside big stages).
+    pub min_radius: f32,
+    pub max_radius: f32,
 }
 
 impl Default for OrbitCamera {
@@ -44,6 +48,8 @@ impl Default for OrbitCamera {
             orbit_sensitivity: 0.005,
             zoom_sensitivity: 0.3,
             pan_sensitivity: 0.003,
+            min_radius: 0.05,
+            max_radius: 500.0,
         }
     }
 }
@@ -54,19 +60,26 @@ fn spawn_camera(mut commands: Commands) {
 
     commands.spawn((
         Camera3d::default(),
+        // Wide near/far so both tiny weapons and multi-thousand-unit stages fit;
+        // the planes are re-scaled to the zoom distance each frame (below).
+        Projection::Perspective(PerspectiveProjection {
+            near: 0.05,
+            far: 100_000.0,
+            ..default()
+        }),
         transform,
         orbit,
     ));
 }
 
 fn orbit_camera(
-    mut query: Query<(&mut OrbitCamera, &mut Transform)>,
+    mut query: Query<(&mut OrbitCamera, &mut Transform, &mut Projection)>,
     mouse_buttons: Res<ButtonInput<MouseButton>>,
     keys: Res<ButtonInput<KeyCode>>,
     mut mouse_motion: EventReader<MouseMotion>,
     mut scroll: EventReader<MouseWheel>,
 ) {
-    let Ok((mut cam, mut transform)) = query.get_single_mut() else { return };
+    let Ok((mut cam, mut transform, mut projection)) = query.get_single_mut() else { return };
 
     let mut delta_motion = Vec2::ZERO;
     for ev in mouse_motion.read() {
@@ -99,13 +112,20 @@ fn orbit_camera(
 
     // Zoom (scroll)
     cam.radius -= scroll_delta * cam.zoom_sensitivity * cam.radius;
-    cam.radius = cam.radius.clamp(0.5, 50.0);
+    cam.radius = cam.radius.clamp(cam.min_radius, cam.max_radius);
 
     // Reset (R key)
     if keys.just_pressed(KeyCode::KeyR) {
         *cam = OrbitCamera::default();
     }
 
+    // Keep the clip planes proportional to the zoom distance so depth precision
+    // stays usable across scales (tiny prop → whole stage grid).
+    if let Projection::Perspective(p) = projection.as_mut() {
+        p.near = (cam.radius * 0.02).clamp(0.02, 50.0);
+        p.far = (cam.radius * 50.0).max(2000.0);
+    }
+
     *transform = orbit_transform(&cam);
 }