chore: drop brand names and orphaned PICK_HIGHLIGHT colours

Neutralise vendor references in comments to plain behavioural descriptions
(object acquisition / object snap). Remove the PICK_HIGHLIGHT and
PICK_HIGHLIGHT_DIM wire colours: their only consumer was the stripped
storm-sewer add-on, and the retained plugin acquisition pathway draws the
ObjectPick snap glyph and per-command hover previews instead, so the
constants are dead.

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

src/scene/mod.rs

@@ -145,8 +145,8 @@ pub fn build_derived_caches(doc: &CadDocument) -> DerivedCaches {
     // Header `$EXTMIN`/`$EXTMAX` is the fast path, but it's untrustworthy:
     // the sentinel (1e20 / -1e20) when the writer never computed extents,
     // stale values when a drawing was edited and extents weren't refreshed,
-    // and Civil-3D-style top-level extents that span only an Insert's
-    // bounding box rather than the actual MSPACE geometry. Any of those
+    // and top-level extents that span only an Insert's bounding box rather
+    // than the actual MSPACE geometry. Any of those
     // leave the precision-preserving offset wrong, so direct MSPACE
     // entities render at huge magnitudes and f32 wires lose precision.
     //