perf(scene): frustum-cull wires using camera view AABB

Block defns and top-level entities now know their world-space XY
AABB, and `tessellate_entity` / `expand_insert` early-out for anything
that doesn't intersect the camera's view rect. Tested commit-only on
time_open (correct subset emitted with default camera); GUI run
pending user verification.

Cache plumbing:
  - `LocalWire` / `BlockDefn` carry `aabb_local` (post-build recursive
    union over nested defns).
  - `Scene::view_world_aabb()` derives a 25%-margined world rect from
    the active camera + last-seen render aspect.
  - `wire_cache` / `paper_sheet_cache` keys widen to
    `(geometry_epoch, camera_generation)` so pan/zoom invalidates the
    cached wire list — and pipeline `cached_epoch` widens to match
    so the GPU re-uploads on view change.
  - `XrefStatus::Unloaded` ack already shipped — orthogonal to this.

Also adds `examples/xref_states.rs` to dump per-block_record xref
metadata for diagnosing the is_loaded / unloaded distinction.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/scene/pipeline/mod.rs

@@ -65,9 +65,10 @@ pub struct Pipeline {
     gpu_face3d_fill: Option<Face3DGpu>,
     gpu_face3d_edges: Vec<WireGpu>,
     pub viewcube: ViewCubePipeline,
-    /// Last geometry epoch for which GPU buffers were uploaded.
-    /// Initialized to u64::MAX so the first frame always uploads.
-    pub cached_epoch: u64,
+    /// Last `(geometry_epoch, camera_generation)` value for which GPU buffers
+    /// were uploaded. We re-upload when either side changes — pan/zoom bumps
+    /// camera_generation, which triggers re-culling and a fresh upload.
+    pub cached_epoch: (u64, u64),
 }
 
 impl Pipeline {
@@ -595,7 +596,7 @@ impl Pipeline {
             gpu_face3d_fill: None,
             gpu_face3d_edges: vec![],
             viewcube,
-            cached_epoch: u64::MAX,
+            cached_epoch: (u64::MAX, u64::MAX),
         }
     }