fix(scene): skip Block/BlockEnd sentinels in wires_for_block filter

Block and BlockEnd are block-defn markers, not drawable geometry.
wires_for_block did not filter them, so they fell through to
legacy_geometry's `_` arm and emitted a 1-unit phantom horizontal
segment at world_offset. The phantom was invisible on a real drawing
but selectable and — worse — its points poisoned fit_all, contributing
to the "ZOOM EXTENTS shrinks the model" symptom on files with weak
EXTMIN/EXTMAX or with block-defn entities leaking into MSPACE.

Same skip already exists in commands.rs:5364 and block_cache.rs:271 —
the render path was the missing one.

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

src/scene/mod.rs

@@ -1012,6 +1012,13 @@ impl Scene {
                 if c.invisible {
                     return false;
                 }
+                // Block/BlockEnd are block-defn sentinels, not drawable geometry.
+                // Without this skip they fall through to legacy_geometry's `_`
+                // arm and emit a 1-unit phantom segment at world_offset that
+                // poisons fit_all and shows up in selection.
+                if matches!(e, EntityType::Block(_) | EntityType::BlockEnd(_)) {
+                    return false;
+                }
                 if self
                     .document
                     .layers