perf(scene): skip wire GPU re-upload when only the camera moved

Phase 3.2 (wire pan path). Wire vertex buffers are world-space, so a
camera move changes only the view_proj uniform (uploaded every frame),
never the wire data — yet upload_wires re-ran on every camera_generation
tick, re-packing vertices and re-writing the GPU buffer on each pan.

Stamp every Model-tile re-tessellation with a monotonic content id
(WIRE_CONTENT_GEN), reused when a pan reuses the tessellation. The
pipeline records the resident buffer's id and skips upload_wires when the
incoming id matches. The gate is pulled out of the (epoch, camera_gen)
block so a preview/interim wire change still uploads even with a static
camera; non-tile paths and overlay frames force a fresh id, preserving
current behaviour. Monotonic id sidesteps the ABA hazard a freed/realloc'd
Arc pointer would carry.

Pairs with the pan tessellation reuse: a pan now skips both the CPU
re-tessellation and the GPU wire upload.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/scene/pipeline/mod.rs

@@ -116,6 +116,12 @@ pub struct Pipeline {
     /// 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),
+    /// Content id of the wire buffer currently resident on the GPU (Phase
+    /// 3.2). When the incoming `ViewportData.wire_content_id` matches, the
+    /// world-space wire vertices are unchanged (e.g. a pure pan reused the
+    /// Model-tile tessellation) and `upload_wires` is skipped. `u64::MAX` =
+    /// nothing uploaded yet.
+    pub cached_wire_id: u64,
 }
 
 impl Pipeline {
@@ -884,6 +890,7 @@ impl Pipeline {
             gpu_face3d_edges: vec![],
             viewcube,
             cached_epoch: (u64::MAX, u64::MAX),
+            cached_wire_id: u64::MAX,
         }
     }